Integrate with uci to support 'enabled/disabled' startup option and
override netify's default auto network selection.

config netifyd
       option enabled 0
       option autoconfig 1

autoconfig: Use netify's in-built interface selection
else use 'internal/external_if' definitions.

Also persist important agent config across sysupgrade
agent.uuid, serial.uuid, site.uuid

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>