silent_call: use osmo_strlcpy() instead of strncpy()

If gsm_silent_call_start() is called with an over long string in
traffic_dst_ip, then the target string might be left unterminated. Lets
use osmo_strlcpy() so that we can be sure the result in scd->traffic_ip
is always terminated.

Fixes: CID#196068
Change-Id: Ic81842175e412ae7d97d023b612412f33411d60c
1 file changed