mgcp: transit is a signed variable and should be printed like this

On AMD64 we had a difference in the test result most likely due
the bigger size of integers.
diff --git a/openbsc/tests/mgcp/mgcp_test.c b/openbsc/tests/mgcp/mgcp_test.c
index b1bbb7f..fdb1890 100644
--- a/openbsc/tests/mgcp/mgcp_test.c
+++ b/openbsc/tests/mgcp/mgcp_test.c
@@ -830,7 +830,7 @@
 		       state.in_stream.err_ts_counter - last_in_ts_err_cnt,
 		       state.out_stream.err_ts_counter - last_out_ts_err_cnt);
 
-		printf("Stats: Jitter = %u, Transit = %u\n",
+		printf("Stats: Jitter = %u, Transit = %d\n",
 		       mgcp_state_calc_jitter(&state), state.transit);
 
 		last_in_ts_err_cnt = state.in_stream.err_ts_counter;