NSH library: Add a Telnetd command. This is needed when network initialization is deferred. In that case, telnet daemon cannot be started until the network is finally initialized. The telnetd command was added just for that case: So that the telnet daemon can be started from the NSH command line after the network is configured.

nshlib/nsh_command.c

@@ -472,6 +472,10 @@ static const struct cmdmap_s g_cmdmap[] =
   { "test",     cmd_test,     3, CONFIG_NSH_MAXARGUMENTS, "<expression>" },
 #endif
 
+#if defined(CONFIG_NSH_TELNET) && !defined(CONFIG_NSH_DISABLE_TELNETD)
+  {"telnetd",   cmd_telnetd,  1, 1, NULL },
+#endif
+
 #ifndef CONFIG_NSH_DISABLE_TIME
   { "time",     cmd_time,     2, 2, "\"<command>\"" },
 #endif