tftpd: make it emit error packets

telnetd: use login always, not "sometimes login, sometimes shell"

   text    data     bss     dec     hex filename
 797612     641    7380  805633   c4b01 busybox_old
 797695     641    7380  805716   c4b54 busybox_unstripped

networking/telnetd.c

@@ -56,11 +56,7 @@ enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
 /* Globals */
 static int maxfd;
 static struct tsession *sessions;
-#if ENABLE_LOGIN
 static const char *loginpath = "/bin/login";
-#else
-static const char *loginpath = DEFAULT_SHELL;
-#endif
 static const char *issuefile = "/etc/issue.net";