Fix memory leak in test_channelpadding_consensus().

The relay variable is always allocated, but might not be freed before we
return from this function.

See: Coverity CID 1437431

src/test/test_channelpadding.c

@@ -745,6 +745,8 @@ test_channelpadding_consensus(void *arg)
   tt_i64_op(val, OP_LE, 24*60*60*2);
 
  done:
+  tor_free(relay);
+
   free_mock_consensus();
   free_fake_channeltls((channel_tls_t*)chan);
   smartlist_free(connection_array);