keep some internal statistics inside OpenBSC

the statistics will give us some idea about the network load and
performance.
diff --git a/openbsc/src/gsm_04_08_utils.c b/openbsc/src/gsm_04_08_utils.c
index e96a1ca..2cd571e 100644
--- a/openbsc/src/gsm_04_08_utils.c
+++ b/openbsc/src/gsm_04_08_utils.c
@@ -488,6 +488,8 @@
 	sig_data.bts	= msg->lchan->ts->trx->bts;
 	sig_data.lchan	= msg->lchan;
 
+	bts->network->stats.paging.completed++;
+
 	dispatch_signal(SS_PAGING, S_PAGING_COMPLETED, &sig_data);
 
 	/* Stop paging on the bts we received the paging response */