In preparation of changing the type of some parameters
of some test functions from `char *` to `data_t` to get
rid of the calls to mbedtls_test_unhexify():
- Align the name of source data length local variable
with the name of the local variable containing the
source data, respectively src_str and src_str_len.
- Change the type of length, index local variables
from int to size_t.
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
e85a2c30bd