osmo-nitb: generate backtrace on SIGABRT

As the NITB has an internal SIGABRT handler that prints a talloc report,
let's also print a stack backtrace at the same point.

Change-Id: Ia63aa5c39b26e27c3ee220d755c17d2c1ef636c5

openbsc/src/osmo-nitb/bsc_hack.c

@@ -209,6 +209,7 @@ static void signal_handler(int signal)
 		exit(0);
 		break;
 	case SIGABRT:
+		osmo_generate_backtrace();
 		/* in case of abort, we want to obtain a talloc report
 		 * and then return to the caller, who will abort the process */
 	case SIGUSR1: