paging: Provide the number of pending requests

Address the FIXME and take code from the on-waves/bsc-master
branch. This will count the number of requests.
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index e052bda..5a4bd6e 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -258,7 +258,8 @@
 	net_dump_nmstate(vty, &bts->nm_state);
 	vty_out(vty, "  Site Mgr NM State: ");
 	net_dump_nmstate(vty, &bts->site_mgr.nm_state);
-	vty_out(vty, "  Paging: FIXME pending requests, %u free slots%s",
+	vty_out(vty, "  Paging: %u pending requests, %u free slots%s",
+		paging_pending_requests_nr(bts),
 		bts->paging.available_slots, VTY_NEWLINE);
 	if (is_ipaccess_bts(bts)) {
 		vty_out(vty, "  OML Link state: %s.%s",