ns: Add statistics for some events

The following counters are added to the ns.nsvc counter group:
  lost.alive             The number of missing ALIVE ACK messages
  lost.reset             The number of missing RESET ACK messages

The following items are added to the ns.nsvc stat item group:
  alive.delay            The time in ms between sending ALIVE and
                         receiving the next ALIVE ACK

Sponsored-by: On-Waves ehf
diff --git a/src/gb/gprs_ns_vty.c b/src/gb/gprs_ns_vty.c
index 155e1e9..5a951dc 100644
--- a/src/gb/gprs_ns_vty.c
+++ b/src/gb/gprs_ns_vty.c
@@ -167,8 +167,10 @@
 			inet_ntoa(nsvc->ip.bts_addr.sin_addr),
 			ntohs(nsvc->ip.bts_addr.sin_port));
 	vty_out(vty, "%s", VTY_NEWLINE);
-	if (stats)
+	if (stats) {
 		vty_out_rate_ctr_group(vty, " ", nsvc->ctrg);
+		vty_out_stat_item_group(vty, " ", nsvc->statg);
+	}
 }
 
 static void dump_ns(struct vty *vty, struct gprs_ns_inst *nsi, int stats)