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_network.c b/openbsc/src/libmgcp/mgcp_network.c
index b15d6f7..2142264 100644
--- a/openbsc/src/libmgcp/mgcp_network.c
+++ b/openbsc/src/libmgcp/mgcp_network.c
@@ -296,6 +296,7 @@
 
 	proto = fd == &endp->net_end.rtp ? PROTO_RTP : PROTO_RTCP;
 	endp->net_end.packets += 1;
+	endp->net_end.octets += rc;
 
 	forward_data(fd->fd, &endp->taps[MGCP_TAP_NET_IN], buf, rc);
 	if (endp->is_transcoded)
@@ -374,6 +375,7 @@
 
 	/* do this before the loop handling */
 	endp->bts_end.packets += 1;
+	endp->bts_end.octets += rc;
 
 	forward_data(fd->fd, &endp->taps[MGCP_TAP_BTS_IN], buf, rc);
 	if (endp->is_transcoded)