Add counters: pcu.bts.N.pch.requests.timeout

Implement T3113 for paging over PCH with default value of 7s (same as
T3113 in OsmoBSC). Increase the new counter on timeout.

Related: SYS#4878
Change-Id: I97475c3dbe2cf00b9cbfec39e93a3c65cb7f749f
diff --git a/src/bts_pch_timer.h b/src/bts_pch_timer.h
new file mode 100644
index 0000000..91bebed
--- /dev/null
+++ b/src/bts_pch_timer.h
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2021 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * Author: Oliver Smith
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/timer.h>
+#include <osmocom/gsm/protocol/gsm_23_003.h>
+
+#include <bts.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct bts_pch_timer {
+	struct llist_head entry;
+	struct gprs_rlcmac_bts *bts;
+	struct osmo_timer_list T3113;
+	char imsi[OSMO_IMSI_BUF_SIZE];
+};
+
+void bts_pch_timer_start(struct gprs_rlcmac_bts *bts, const char *imsi);
+void bts_pch_timer_stop(struct gprs_rlcmac_bts *bts, const char *imsi);
+
+#ifdef __cplusplus
+}
+#endif