bts: Introduce a PollController that has the responsibility to poll

For each frame indication received by the BTS the poll controller
is asked to expire timedout entries.
diff --git a/src/poll_controller.cpp b/src/poll_controller.cpp
new file mode 100644
index 0000000..59eef76
--- /dev/null
+++ b/src/poll_controller.cpp
@@ -0,0 +1,62 @@
+/* poll_controller.h
+ *
+ * Copyright (C) 2012 Andreas Eversberg <jolly@eversberg.eu>
+ * Copyright (C) 2013 by Holger Hans Peter Freyther
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 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/>.
+ *
+ */
+
+#include <poll_controller.h>
+#include <tbf.h>
+
+PollController::PollController(BTS& bts)
+	: m_bts(bts)
+{}
+
+void PollController::expireTimedout(int frame_number)
+{
+	struct gprs_rlcmac_bts *bts = m_bts.bts_data();
+	struct gprs_rlcmac_tbf *tbf;
+	struct gprs_rlcmac_sba *sba, *sba2;
+	uint32_t elapsed;
+
+	/* check for poll timeout */
+	llist_for_each_entry(tbf, &gprs_rlcmac_ul_tbfs, list) {
+		if (tbf->poll_state == GPRS_RLCMAC_POLL_SCHED) {
+			elapsed = (frame_number + 2715648 - tbf->poll_fn)
+								% 2715648;
+			if (elapsed >= 20 && elapsed < 2715400)
+				gprs_rlcmac_poll_timeout(bts, tbf);
+		}
+	}
+	llist_for_each_entry(tbf, &gprs_rlcmac_dl_tbfs, list) {
+		if (tbf->poll_state == GPRS_RLCMAC_POLL_SCHED) {
+			elapsed = (frame_number + 2715648 - tbf->poll_fn)
+								% 2715648;
+			if (elapsed >= 20 && elapsed < 2715400)
+				gprs_rlcmac_poll_timeout(bts, tbf);
+		}
+	}
+	llist_for_each_entry_safe(sba, sba2, &gprs_rlcmac_sbas, list) {
+		elapsed = (frame_number + 2715648 - sba->fn) % 2715648;
+		if (elapsed >= 20 && elapsed < 2715400) {
+			/* sba will be freed here */
+			gprs_rlcmac_sba_timeout(sba);
+		}
+	}
+
+}