Add constants for additional ICMPv6 types
Add constants for additional ICMPv6 types

Introducing additional constants for ICMPv6 types so integer literal
types can be removed in Neutron.

Change-Id: I9caa234304fb621aa9ec0ab8156968b746a6b24a

openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib,openstack/neutron-lib