By popular request reinstate fakeidentd's standalone mode.

Since this is also needed for other applets like telnetd,
introduce generic driver for such things.
It even supports inetd-wait ('linger') mode, when inetd
hands out listen socket to child and waits to it to die,
instead of handing out accepted socket and continuing
listening itself (nowait mode).
Code growth ~200 bytes.
NB: our inetd doesn't support wait mode yet (or mabe it is buggy).

networking/inetd.c

@@ -1289,31 +1289,28 @@ inetd_main(int argc, char *argv[])
 	if (CONFIG == NULL)
 		bb_error_msg_and_die("non-root must specify a config file");
 
-	if (!(opt & 2)) {
 #ifdef BB_NOMMU
+	if (!(opt & 2)) {
 		/* reexec for vfork() do continue parent */
 		vfork_daemon_rexec(0, 0, argc, argv, "-f");
-#else
-		xdaemon(0, 0);
-#endif
-	} else {
-		setsid();
 	}
+	bb_sanitize_stdio(0);
+#else
+	bb_sanitize_stdio(!(opt & 2));
+#endif
 	logmode = LOGMODE_SYSLOG;
 
 	if (uid == 0) {
-		gid_t gid = getgid();
-
 		/* If run by hand, ensure groups vector gets trashed */
+		gid_t gid = getgid();
 		setgroups(1, &gid);
 	}
 
 	{
 		FILE *fp = fopen(_PATH_INETDPID, "w");
-
 		if (fp != NULL) {
 			fprintf(fp, "%u\n", getpid());
-			(void) fclose(fp);
+			fclose(fp);
 		}
 	}