TBF: unify timer handling

Use generic timer handling infrastracture to handle assignment/reject
internal timer. Rename timer array accordingly. Use defines with
explicit second/microsecond values to make it more readable.

Change-Id: I63fb7e6f0695383a83472c836a381a055f64690b
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index b043989..33eb75b 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -484,7 +484,6 @@
 void gprs_rlcmac_dl_tbf::trigger_ass(struct gprs_rlcmac_tbf *old_tbf)
 {
 	/* stop pending timer */
-	stop_timer("assignment (DL-TBF)");
 	stop_timers("assignment (DL-TBF)");
 
 	/* check for downlink tbf:  */
@@ -499,7 +498,7 @@
 			state_flags |= (1 << GPRS_RLCMAC_FLAG_PACCH);
 
 		/* start timer */
-		tbf_timer_start(this, 0, Tassign_pacch, "assignment (PACCH)");
+		t_start(T0, T_ASS_PACCH_SEC, 0, "assignment (PACCH)", true);
 	} else {
 		LOGPTBFDL(this, LOGL_DEBUG, "Send dowlink assignment on PCH, no TBF exist (IMSI=%s)\n",
 			  imsi());