libotr: Fix build of tests/regression/client/client.c

Until this is fixed upstream, have a downstream fix so libotr can be
merged.

pkgs/development/libraries/libotr/default.nix

@@ -9,6 +9,8 @@ stdenv.mkDerivation rec {
     sha256 = "1x8rliydhbibmzwdbyr7pd7n87m2jmxnqkpvaalnf4154hj1hfwb";
   };
 
+  patches = [ ./fix-regtest-client.patch ];
+
   outputs = [ "bin" "out" "dev" ];
 
   nativeBuildInputs = [ autoreconfHook ];

pkgs/development/libraries/libotr/fix-regtest-client.patch

@@ -0,0 +1,11 @@
+diff -Nur a/tests/regression/client/client.c b/tests/regression/client/client.c
+--- a/tests/regression/client/client.c	2015-12-25 17:39:45.000000000 +0000
++++ b/tests/regression/client/client.c	2022-03-29 19:33:18.646398117 +0100
+@@ -27,6 +27,7 @@
+ #include <syscall.h>
+ #include <sys/epoll.h>
+ #include <sys/types.h>
++#include <sys/socket.h>
+ #include <sys/un.h>
+ #include <unistd.h>
+