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/tbf.cpp b/src/tbf.cpp
index b99c521..672c296 100644
--- a/src/tbf.cpp
+++ b/src/tbf.cpp
@@ -45,6 +45,12 @@
 
 static void tbf_timer_cb(void *_tbf);
 
+const struct value_string gprs_rlcmac_tbf_poll_state_names[] = {
+	OSMO_VALUE_STRING(GPRS_RLCMAC_POLL_NONE),
+	OSMO_VALUE_STRING(GPRS_RLCMAC_POLL_SCHED), /* a polling was scheduled */
+	{ 0, NULL }
+};
+
 const struct value_string gprs_rlcmac_tbf_dl_ass_state_names[] = {
 	OSMO_VALUE_STRING(GPRS_RLCMAC_DL_ASS_NONE),
 	OSMO_VALUE_STRING(GPRS_RLCMAC_DL_ASS_SEND_ASS),
@@ -172,7 +178,6 @@
 	first_ts(0),
 	first_common_ts(0),
 	control_ts(0xff),
-	poll_state(GPRS_RLCMAC_POLL_NONE),
 	poll_fn(0),
 	poll_ts(0),
 	n3105(0),
@@ -192,6 +197,7 @@
 	dl_ass_state(GPRS_RLCMAC_DL_ASS_NONE),
 	ul_ass_state(GPRS_RLCMAC_UL_ASS_NONE),
 	ul_ack_state(GPRS_RLCMAC_UL_ACK_NONE),
+	poll_state(GPRS_RLCMAC_POLL_NONE),
 	m_list(this),
 	m_ms_list(this),
 	m_egprs_enabled(false)