Simplify polling troubleshooting

* introduce enum describing poll kind and use it in set_polling()
* move state change into set_polling()
* move logging into set_polling() and unify output
* move duplicated code into static function
* adjust tests to match unified logging output

Change-Id: I14074207f8bbc18b3ebd60875bb99a0a3a4b399d
Related: OS#1524
diff --git a/src/bts.cpp b/src/bts.cpp
index 0f67536..add6ab3 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -1381,7 +1381,9 @@
 		}
 
 		/* set control ts to current MS's TS, until assignment complete */
-		LOGP(DRLCMAC, LOGL_DEBUG, "Change control TS to %d until assinment is complete.\n", ts_no);
+		LOGP(DRLCMAC, LOGL_DEBUG, "%s change control TS %d -> %d until assinment is complete.\n",
+		     tbf_name(ul_tbf), ul_tbf->control_ts, ts_no);
+
 		ul_tbf->control_ts = ts_no;
 		/* schedule uplink assignment */
 		ul_tbf->ul_ass_state = GPRS_RLCMAC_UL_ASS_SEND_ASS;