controller: add ipv6 prefix delegation state machine

Introduce IPv6 Prefix delegation state machine according to RFC 3633
https://tools.ietf.org/html/rfc3633.
Add handle_dhcpv6_reply controller action to parse advertise/reply from
IPv6 delegation server. Advertise/reply are parsed running respectively:
- pinctrl_parse_dhcv6_advt
- pinctrl_parse_dhcv6_reply
The IPv6 requesting router starts sending dhcpv6 solicit through the logical
router port marked with ipv6_prefix_delegation set to true.
An IPv6 prefix will be requested for each logical router port marked
with "prefix" set to true in option column of logical router port table.
Save IPv6 prefix received by IPv6 delegation router in the options columns of
SB port binding table in order to be reused by Router Advertisement framework
run by ovn logical router pipeline.
IPv6 Prefix delegation state machine is enabled on Gateway Router or on
a Gateway Router Port

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: 0-day Robot <robot@bytheb.org>