Add new f_timer_safe_restart() function for warning-safe restart

TITAN will print warnings if a still-running timer is res-started.
It will also warn if a not-started timer is stopped, so we need
a conditional stop + start if we want to avoid any warnings in a
convenient way.

Change-Id: Iee83b4905cce3a84eb007ffd189b55f4b54f7cb6
diff --git a/bts/BTS_Tests.ttcn b/bts/BTS_Tests.ttcn
index 9cb0f72..8800139 100644
--- a/bts/BTS_Tests.ttcn
+++ b/bts/BTS_Tests.ttcn
@@ -544,8 +544,7 @@
 	alt {
 	[] RSL_CCHAN.receive(tr_RSL_UD(tr_RSL_CHAN_RQD(?,?))) {
 		rsl_chrqd := rsl_chrqd + 1;
-		T.stop;
-		T.start;
+		f_timer_safe_restart(T);
 		repeat;
 		}
 	[] RSL_CCHAN.receive { repeat; }
@@ -732,7 +731,7 @@
 		/* increment counter of next to-be-expected meas rep */
 		g_next_meas_res_nr := (g_next_meas_res_nr + 1) mod 256;
 		/* Re-start the timer expecting the next MEAS RES */
-		g_Tmeas_exp.start;
+		f_timer_safe_restart(g_Tmeas_exp);
 		repeat;
 		}
 	[] RSL.receive(tr_RSL_MEAS_RES(g_chan_nr, g_next_meas_res_nr)) -> value rsl {