TBF: expand timer logging

* log timer values
* log start/stop cause
* update test output as necessary

This simplifies debugging issues with TBF timers.

Related: OS#2407
Change-Id: Ib8e537416af9bec5d447356286f44e9e8bbf1b7a
diff --git a/src/tbf.h b/src/tbf.h
index e9d8df8..80249df 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -174,7 +174,7 @@
 
 	int update();
 	void handle_timeout();
-	void stop_timer();
+	void stop_timer(const char *reason);
 	void stop_t3191();
 	int establish_dl_tbf_on_pacch();
 
@@ -330,7 +330,7 @@
 int tbf_assign_control_ts(struct gprs_rlcmac_tbf *tbf);
 
 void tbf_timer_start(struct gprs_rlcmac_tbf *tbf, unsigned int T,
-                        unsigned int seconds, unsigned int microseconds);
+		     unsigned int seconds, unsigned int microseconds, const char *reason);
 
 inline bool gprs_rlcmac_tbf::state_is(enum gprs_rlcmac_tbf_state rhs) const
 {