NIC Bridge allow IP Aliases / IP filtering

[monkz]

Issue description

Interfaces usually allowed to have more than one IP addresses - IP alias In the current state of the code just one IPv4 and/or one IPv6 address can be assigned. https://linuxcontainers.org/lxd/docs/master/instances/#nic-bridged https://github.com/lxc/lxd/blob/a5814e4374c85700774e1a76014d28a1910e07c4/lxd/device/nic_bridged.go#L77 https://github.com/lxc/lxd/blob/a5814e4374c85700774e1a76014d28a1910e07c4/lxd/device/nic_bridged.go#L78

If IP filtering is activated this limitation restricts the use of the interface to one IP address per AF. https://github.com/lxc/lxd/blob/a5814e4374c85700774e1a76014d28a1910e07c4/lxd/device/nic_bridged.go#L84 https://github.com/lxc/lxd/blob/a5814e4374c85700774e1a76014d28a1910e07c4/lxd/device/nic_bridged.go#L85

This limits the use of virtual IP adresses via software like heartbeat / pacemaker / ....

Possible Solution

Accept a comma separated list of IPv4 and IPv6 Addresses, either on ipvX.address or create an other attribute like ipvX.addresses (to use the plural form of that attribute) and use all IP addresses on security.ipvX_filtering.

[tomponline]

We already accept multiple ips as comma delimited list for routed NICs. Whilst bridged NICs can only use a single ip for dhcp allocation, it could make sense to allow multiple when using ip filtering. And only take the first one for dhcp.