TBF: make poll state internal

* add functions/macros for setting TBF's poll state
* add function for checking TBF's poll state

Change-Id: I6db1c4e7bd0a49aeb5e391afe371c36b96c6a702
Related: OS#1539
diff --git a/src/poll_controller.cpp b/src/poll_controller.cpp
index f8ab6c9..5c5a717 100644
--- a/src/poll_controller.cpp
+++ b/src/poll_controller.cpp
@@ -47,14 +47,14 @@
 
 	llist_for_each(pos, &m_bts.ul_tbfs()) {
 		ul_tbf = as_ul_tbf(pos->entry());
-		if (ul_tbf->poll_state == GPRS_RLCMAC_POLL_SCHED) {
+		if (ul_tbf->poll_scheduled()) {
 			if (elapsed_fn_check(max_delay, frame_number, ul_tbf->poll_fn))
 				ul_tbf->poll_timeout();
 		}
 	}
 	llist_for_each(pos, &m_bts.dl_tbfs()) {
 		dl_tbf = as_dl_tbf(pos->entry());
-		if (dl_tbf->poll_state == GPRS_RLCMAC_POLL_SCHED) {
+		if (dl_tbf->poll_scheduled()) {
 			if (elapsed_fn_check(max_delay, frame_number, dl_tbf->poll_fn))
 				dl_tbf->poll_timeout();
 		}