Disable fragmentation tests with openssl bugs

While making the initial commit, I thought $OPENSSL_LEGACY was not affect by
this bug, but it turns out I was wrong. All versions of OpenSSL installed on
the CI are. Therefore, the corresponding tests are disabled for the same
reason as the gnutls-cli tests above it.

This commit is only about the tests that were added in the recent
fragmentation work. One of those two tests had a particularly
annoying mode of failure: it failed consistently with seed=1 (use in the
release version of all.sh), once #1951 was applied. This has nothing
particular to do with #1951, except that by changing retransmission behaviour
1951 made the proxy run into a path that triggered the OpenSSL bug with this
seed, while it previously did that only with other seeds.

Other 3d interop test are also susceptible to triggering this OpenSSL bug or
others (or bugs in GnuTLS), but they are left untouched by this commit as:
- they were pre-existing to the recent DTLS branches;
- they don't seem to have the particularly annoying seed=1 mode of failure.
However it's probably desirable to do something about them at some point in
the future.

tests/ssl-opt.sh

@@ -5746,13 +5746,11 @@ run_test    "DTLS fragmenting: 3d, gnutls client, DTLS 1.0" \
             0 \
             -s "fragmenting handshake message"
 
-## Interop test with OpenSSL might triger a bug in recent versions (that
-## probably won't be fixed before 1.1.1X), so we use an old version that
-## doesn't have this bug, but unfortunately it doesn't have support for DTLS
-## 1.2 either, so the DTLS 1.2 tests are commented for now.
+## Interop test with OpenSSL might trigger a bug in recent versions (including
+## all versions installed on the CI machines), reported here:
 ## Bug report: https://github.com/openssl/openssl/issues/6902
-## They should be re-enabled (and the DTLS 1.0 switched back to a non-legacy
-## version of OpenSSL once a fixed version of OpenSSL is available)
+## They should be re-enabled once a fixed version of OpenSSL is available
+## (this should happen in some 1.1.1_ release according to the ticket).
 skip_next_test
 requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
 requires_config_enabled MBEDTLS_RSA_C
@@ -5770,7 +5768,7 @@ run_test    "DTLS fragmenting: 3d, openssl server, DTLS 1.2" \
             -c "fragmenting handshake message" \
             -C "error"
 
-requires_openssl_legacy
+skip_next_test
 requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
 requires_config_enabled MBEDTLS_RSA_C
 requires_config_enabled MBEDTLS_ECDSA_C
@@ -5778,7 +5776,7 @@ requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_1
 client_needs_more_time 4
 run_test    "DTLS fragmenting: 3d, openssl server, DTLS 1.0" \
             -p "$P_PXY drop=8 delay=8 duplicate=8" \
-            "$O_LEGACY_SRV -dtls1 -verify 10" \
+            "$O_SRV -dtls1 -verify 10" \
             "$P_CLI dgram_packing=0 dtls=1 debug_level=2 \
              crt_file=data_files/server8_int-ca2.crt \
              key_file=data_files/server8.key \
@@ -5787,25 +5785,25 @@ run_test    "DTLS fragmenting: 3d, openssl server, DTLS 1.0" \
             -c "fragmenting handshake message" \
             -C "error"
 
-## see comment on the previous-previous test
-## requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
-## requires_config_enabled MBEDTLS_RSA_C
-## requires_config_enabled MBEDTLS_ECDSA_C
-## requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_2
-## client_needs_more_time 4
-## run_test    "DTLS fragmenting: 3d, openssl client, DTLS 1.2" \
-##             -p "$P_PXY drop=8 delay=8 duplicate=8" \
-##             "$P_SRV dtls=1 debug_level=2 \
-##              crt_file=data_files/server7_int-ca.crt \
-##              key_file=data_files/server7.key \
-##              hs_timeout=250-60000 mtu=512 force_version=dtls1_2" \
-##             "$O_CLI -dtls1_2" \
-##             0 \
-##             -s "fragmenting handshake message"
+skip_next_test
+requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
+requires_config_enabled MBEDTLS_RSA_C
+requires_config_enabled MBEDTLS_ECDSA_C
+requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_2
+client_needs_more_time 4
+run_test    "DTLS fragmenting: 3d, openssl client, DTLS 1.2" \
+            -p "$P_PXY drop=8 delay=8 duplicate=8" \
+            "$P_SRV dtls=1 debug_level=2 \
+             crt_file=data_files/server7_int-ca.crt \
+             key_file=data_files/server7.key \
+             hs_timeout=250-60000 mtu=512 force_version=dtls1_2" \
+            "$O_CLI -dtls1_2" \
+            0 \
+            -s "fragmenting handshake message"
 
 # -nbio is added to prevent s_client from blocking in case of duplicated
 # messages at the end of the handshake
-requires_openssl_legacy
+skip_next_test
 requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
 requires_config_enabled MBEDTLS_RSA_C
 requires_config_enabled MBEDTLS_ECDSA_C
@@ -5817,7 +5815,7 @@ run_test    "DTLS fragmenting: 3d, openssl client, DTLS 1.0" \
              crt_file=data_files/server7_int-ca.crt \
              key_file=data_files/server7.key \
              hs_timeout=250-60000 mtu=512 force_version=dtls1" \
-            "$O_LEGACY_CLI -nbio -dtls1" \
+            "$O_CLI -nbio -dtls1" \
             0 \
             -s "fragmenting handshake message"