ipv6 support for default-address-pools

[genofire]

It would be really useful if there is multiple subnet support by default.
IPv6 has ULA IP ranges for privacy use ...b

{
  "ipv6": true,
  "fixed-cidr-v6": "2a01::/80", 
  "dns": ["85.214.20.141","2a01:238:42f6:ac00:2a29:4f7f:b6d:ef46"],
  "default-address-pools":[{"scope":"local","base":"fd42:d0ce::/80","size":64}],
}

journald:

Feb 28 18:45:25 server dockerd[868]: time="2019-02-28T18:45:25.397005833+01:00" level=info msg="Loading containers: start."
Feb 28 18:45:25 server dockerd[868]: time="2019-02-28T18:45:25.844677858+01:00" level=info msg="Default bridge (docker0) is assigned with an IP address fd42:d0ce::/80. Daemon option --bip can be used to set a preferred IP addre>
Feb 28 18:45:25 server dockerd[868]: time="2019-02-28T18:45:25.845451299+01:00" level=info msg="stopping event stream following graceful shutdown" error="<nil>" module=libcontainerd namespace=moby
Feb 28 18:45:25 server dockerd[868]: time="2019-02-28T18:45:25.846009422+01:00" level=info msg="stopping healthcheck following graceful shutdown" module=libcontainerd
Feb 28 18:45:25 server dockerd[868]: time="2019-02-28T18:45:25.846021643+01:00" level=info msg="stopping event stream following graceful shutdown" error="context canceled" module=libcontainerd namespace=plugins.moby
Feb 28 18:45:25 server dockerd[868]: time="2019-02-28T18:45:25.846535294+01:00" level=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc0006fee30, TRANSIENT_FAILURE" module=grpc
Feb 28 18:45:25 server dockerd[868]: time="2019-02-28T18:45:25.848417068+01:00" level=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc0006fee30, CONNECTING" module=grpc
Feb 28 18:45:26 server dockerd[868]: Error starting daemon: Error initializing network controller: Error creating default "bridge" network: failed to add IPv4 address fd42:d0ce::1/80 to bridge: file exists