pdch_ulc: Store TBF poll reason

This allows easily checking the initial reason to trigger the poll when
either it is received or times out.

Later on this reason can be transformed into an FSM event and sent to
the related FSM.

Related: OS#5020
Change-Id: Ie8fefd1f47ad674ce597a8065b15284088956bde
diff --git a/src/nacc_fsm.c b/src/nacc_fsm.c
index df7cd7d..6384fd5 100644
--- a/src/nacc_fsm.c
+++ b/src/nacc_fsm.c
@@ -206,7 +206,7 @@
 	LOGP(DNACC, LOGL_DEBUG, "------------------------- TX : Packet Cell Change Continue -------------------------\n");
 	rate_ctr_inc(&bts_rate_counters(ms->bts)->ctr[CTR_PKT_CELL_CHG_CONTINUE]);
 	talloc_free(mac_control_block);
-	tbf_set_polling(tbf, *new_poll_fn, data->ts, GPRS_RLCMAC_POLL_CELL_CHG_CONTINUE);
+	tbf_set_polling(tbf, *new_poll_fn, data->ts, PDCH_ULC_POLL_CELL_CHG_CONTINUE);
 	return msg;
 
 free_ret: