Implement optional syslog logging using ordinary

bb_xx_msg calls, and convert networking/* to it.
The rest of bbox will be converted gradually.

networking/udhcp/signalpipe.c

@@ -36,7 +36,7 @@ static int signal_pipe[2];
 static void signal_handler(int sig)
 {
 	if (send(signal_pipe[1], &sig, sizeof(sig), MSG_DONTWAIT) < 0)
-		DEBUG(LOG_ERR, "Could not send signal: %m");
+		bb_perror_msg("Could not send signal");
 }