mgcp: Count the received octets as of the MGCP specification

Count the received octets. This is encouraged by the MGCP specification.
Use a 32bit counter that is good enough for more than 12 hours of a EFR
call. This limit is good enough for the current configuration.
diff --git a/openbsc/src/libmgcp/mgcp_protocol.c b/openbsc/src/libmgcp/mgcp_protocol.c
index ac7dea1..719a4c7 100644
--- a/openbsc/src/libmgcp/mgcp_protocol.c
+++ b/openbsc/src/libmgcp/mgcp_protocol.c
@@ -897,6 +897,7 @@
 	}
 
 	end->packets = 0;
+	end->octets = 0;
 	memset(&end->addr, 0, sizeof(end->addr));
 	end->rtp_port = end->rtcp_port = 0;
 	end->payload_type = -1;