mgcp/test: Reset pkt_period_* after each test

Currently these value may leak into the next test.

This patch will reset them after each message has been processed.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/tests/mgcp/mgcp_test.c b/openbsc/tests/mgcp/mgcp_test.c
index 7653a0d..538dc9f 100644
--- a/openbsc/tests/mgcp/mgcp_test.c
+++ b/openbsc/tests/mgcp/mgcp_test.c
@@ -366,6 +366,8 @@
 			endp->net_end.packet_duration_ms = -1;
 			endp->bts_end.output_enabled = 0;
 			endp->net_end.output_enabled = 0;
+			endp->local_options.pkt_period_min = 0;
+			endp->local_options.pkt_period_max = 0;
 			endp->conn_mode = -1;
 		}