isisd: API: basic circuit config

Create isis_vty.c and start moving off CLI functions into that.  These
then call newly-added "nice" API wrappers.

Patch contains significant work authored by Christian Franke.

[v2: removed stuff that crept in from the next patch]

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
6 files changed