- remnant of libknot separation I guess.

Signed-off-by: Jan Kadlec <jan.kadlec@nic.cz>

Conflicts:
	src/knot/server/udp-handler.c

protocol-agnostic response, copied socket for deferred cleanup
The copy is needed so the TCP worker can close the socket and
the connection is held until the UPDATE request is cleared.

The MSG_WAITALL doesn't work as expected everywhere and
can return partial answer (for example with signal interrupt).
Also implemented timeouts for TCP receive.

Previously, response was paired to query according to the Message ID
and QUESTION. This however doesn't work for zone transfers, as some
servers omit the question section for multi-packet answers
completely.

- The previous function tried to commit diff changes to zone (already
  there) and stored DNSSEC and diff changes unmerged.

Zone events IXFR-in

Honestly I have no idea if this will work for all the corner case that were mentioned in the old code. I think my next step will be to a make a test case for all of them.

Conflicts:
	src/knot/nameserver/axfr.c