When enabled, direct protocol generates routes only if the underlying
link state is up.

The patch adds support for channels, structures connecting protocols and
tables and handling most interactions between them. The documentation is
missing yet.

Based on the patch from Alexander V. Chernikov.
Extended to support almost all protocols.
Uses 'protocol bgp NAME from TEMPLATE { ... }' syntax.

state machines. Full explanation will follow soon.

intended to serve as an example of interface pattern list use. As a side
effect, you can disable generating of device routes by disabling
this protocol.