src: use namespace prefix osmo_timer* for timer functions

Summary of changes:

s/struct timer_list/struct osmo_timer_list/g
s/bsc_add_timer/osmo_timer_add/g
s/bsc_schedule_timer/osmo_timer_schedule/g
s/bsc_del_timer/osmo_timer_del/g
s/bsc_timer_pending/osmo_timer_pending/g
s/bsc_nearest_timer/osmo_timers_nearest/g
s/bsc_prepare_timers/osmo_timers_prepare/g
s/bsc_update_timers/osmo_timers_update/g
s/bsc_timer_check/osmo_timers_check/g
diff --git a/openbsc/src/gprs/sgsn_libgtp.c b/openbsc/src/gprs/sgsn_libgtp.c
index 37d976f..7e66035 100644
--- a/openbsc/src/gprs/sgsn_libgtp.c
+++ b/openbsc/src/gprs/sgsn_libgtp.c
@@ -538,7 +538,7 @@
 	gtp_retranstimeout(sgi->gsn, &next);
 
 	/* re-schedule the timer */
-	bsc_schedule_timer(&sgi->gtp_timer, next.tv_sec, next.tv_usec/1000);
+	osmo_timer_schedule(&sgi->gtp_timer, next.tv_sec, next.tv_usec/1000);
 }
 
 /* timer callback for libgtp retransmissions and ping */