Comment 2 for bug 1378952

Reviewed: https://review.openstack.org/126781
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=8a08a3cb47d0dd69d4aa2e8fa661d04054fe95ae
Submitter: Jenkins
Branch: master

commit 8a08a3cb47d0dd69d4aa2e8fa661d04054fe95ae
Author: Henry Gessau <email address hidden>
Date: Tue Oct 7 20:38:38 2014 -0400

    Disable PUT for IPv6 subnet attributes

    In Juno we are not ready for allowing the IPv6 attributes on a subnet
    to be updated after the subnet is created, because:
    - The implementation for supporting updates is incomplete.
    - Perceived lack of usefulness, no good use cases known yet.
    - Allowing updates causes more complexity in the code.
    - Have not tested that radvd, dhcp, etc. behave OK after update.

    Therefore, for now, we set 'allow_put' to False for the two IPv6
    attributes, ipv6_ra_mode and ipv6_address_mode. This prevents the
    modes from being updated via the PUT:subnets API.

    Closes-bug: #1378952

    Change-Id: Id6ce894d223c91421b62f82d266cfc15fa63ed0e