mgcp: Include statistics at the end of a connection

Follow the MGCP specification and send the collected statistics
at the end of a call. Right now this does not include jitter, packet
loss and delay.
diff --git a/openbsc/tests/mgcp/mgcp_test.ok b/openbsc/tests/mgcp/mgcp_test.ok
index 45882a5..5e0e47c 100644
--- a/openbsc/tests/mgcp/mgcp_test.ok
+++ b/openbsc/tests/mgcp/mgcp_test.ok
@@ -7,4 +7,5 @@
 Testing SHORT2
 Testing SHORT3
 Testing SHORT4
+Testing DLCX
 Done