[Xastir] dual port TNC

[Jason KG4WSV]

Will xastir read from a pipe instead of a serial port device special
file in the TNC interface code?

I had the idea of a simple daemon that would speak MKISS to the TNC,
then break out individual streams over named pipes and let xastir talk
to them.

An alternative idea was to add a KISS network interface, for use with
things like socat et al.  Would allow the MKISS daemon to talk to
network ports instead of named pipes, and has the added benefit of
allowing xastir to talk to network serial ports.

-Jason
kg4wsv