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/gprs_rlcmac_sched.cpp b/src/gprs_rlcmac_sched.cpp
index 3f9fcb1..ebf4714 100644
--- a/src/gprs_rlcmac_sched.cpp
+++ b/src/gprs_rlcmac_sched.cpp
@@ -49,8 +49,7 @@
 		if (ul_tbf->trx->trx_no != trx || !ul_tbf->is_control_ts(ts))
 			continue;
 		/* polling for next uplink block */
-		if (ul_tbf->poll_state == GPRS_RLCMAC_POLL_SCHED
-		 && ul_tbf->poll_fn == poll_fn)
+		if (ul_tbf->poll_scheduled() && ul_tbf->poll_fn == poll_fn)
 			*poll_tbf = ul_tbf;
 		if (ul_tbf->ul_ack_state_is(GPRS_RLCMAC_UL_ACK_SEND_ACK))
 			*ul_ack_tbf = ul_tbf;
@@ -69,8 +68,7 @@
 		if (dl_tbf->trx->trx_no != trx || !dl_tbf->is_control_ts(ts))
 			continue;
 		/* polling for next uplink block */
-		if (dl_tbf->poll_state == GPRS_RLCMAC_POLL_SCHED
-		 && dl_tbf->poll_fn == poll_fn)
+		if (dl_tbf->poll_scheduled() && dl_tbf->poll_fn == poll_fn)
 			*poll_tbf = dl_tbf;
 		if (dl_tbf->dl_ass_state_is(GPRS_RLCMAC_DL_ASS_SEND_ASS))
 			*dl_ass_tbf = dl_tbf;