daemon() has to be called prior to file descriptor setups

(otherwise file descriptors could be closed mistakenly)

Obtained from:	KAME
MFC after:	1 week

usr.sbin/rtadvd/rtadvd.c

@@ -228,11 +228,11 @@ main(argc, argv)
 		fprintf(stderr, "fatal: inet_pton failed\n");
 		exit(1);
 	}
-	sock_open();
-
 	if (!fflag)
 		daemon(1, 0);
 
+	sock_open();
+
 	/* record the current PID */
 	pid = getpid();
 	if ((pidfp = fopen(pidfilename, "w")) == NULL) {