libwebsockets

netlink: migrate to context

For SMP case, it was desirable to have a netlink listener per pt so they
could deal with pt-level changes in the pt's local service thread.  But
Linux restricts the process to just one netlink listener.

We worked around it by only listening on pt[0], this aligns us a bit more
with the reality and moves to a single routing table in the context.
There's still more to do for SMP case locking.