Update old TTL info from RFC 793 with RFC 9293 (TTL used to be 60, but
now it must be configurable).

NOTE the default and maximum value.

Remove also telnet and ftp info (deprecated tools).

Fixes: #488
Closes: #497
Reported-by: Greg Skinner <gds@alum.mit.edu>
Suggested-by: Greg Skinner <gds@alum.mit.edu>
Reviewed-by: Greg Skinner <gds@alum.mit.edu>
Signed-off-by: Petr Vorel <pvorel@suse.cz>