[rfc] add MK_TELNET_SSL as a build option

[Benjamin Kaduk]

On Sat, 13 Jun 2015, Adrian Chadd wrote:

> Hi,
>
> The wifi builds have a need for building telnet/telnetd without
> ssl/kerberos in order to meet size constraints and to allow them to be
> crunch'ed.

Something of a tangent, but the kerberos support in telnet is limited to
single-DES, i.e., breakable for $50 or so.  I, for one, would be fine
seeing it just get removed entirely.  (I have no data about telnet/ssl.)

-Ben