A sad thing is that we does not have a 'router_id' filter type,
so it must be given as decimal number in filters.

And also fixes a minor bug.

Also fixes a bug in the previous patch.

Before this change, protocols were restarted in that case.

Because we don't want to have a limit on a function/filter length.

Process well-known communities before the export filter (old behavior is
to process these attributes after, which does not allow to send route
with such community) and just for routes received from other BGP
protocols. Also fixes a bug in next_hop check.

Opaque pipes are obsolete and should disappear in the future.