Enabling DHCPv6 by default on EC2 leads to instance with broken IPv6
connectivity. AWS provides the IP address via DHCPv6 and SLAAC, but
router advertisements are not accepted if the instance has DHCPv6
configured. The accept_ra value is set to 0.
Removing the `dhcp` option from `ipv6.method` and simply using `auto`
(the default) allows the instance to pick up its IPv6 address and accept
router advertisements from the AWS network.
RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2092459
Pagure: https://pagure.io/cloud-sig/issue/382
Upstream: https://bugs.launchpad.net/cloud-init/+bug/1976526?comments=all
Signed-off-by: Major Hayden <major@redhat.com>
