SSL test programs: enable the PSA test external RNG

Currently, MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG is tested with a dummy
insecure implementation of mbedtls_psa_external_get_random. This
function needs to be explicitly enabled at runtime. This needs to
happen when the PSA external RNG is used, which currently is the case
in SSL test programs only when MBEDTLS_USE_PSA_CRYPTO is enabled.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

programs/ssl/ssl_client2.c

@@ -760,6 +760,9 @@ int main( int argc, char *argv[] )
         ret = MBEDTLS_ERR_SSL_HW_ACCEL_FAILED;
         goto exit;
     }
+#if defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)
+    mbedtls_test_enable_insecure_external_rng( );
+#endif
 #endif
 
     if( argc == 0 )