lxd/network/driver/bridge: Skip lo interface when generating fan overlay address in addressForSubnet
lxd/network/driver/bridge: Skip lo interface when generating fan overlay address in addressForSubnet

Avoids detecting the incorrect fan underlay address when /32 VIPs from the underlay subnet are added to the lo interface.

Also avoids breaking GCP setups that use /32 on the main network underlay interface.

Fixes https://discuss.linuxcontainers.org/t/delete-a-stopped-container-bring-down-the-fan-interface/8803
Fixes https://discuss.linuxcontainers.org/t/lxd-container-stuck-in-running-without-ip-address/8973

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

atxwebs/lxd,stgraber/lxd,stgraber/lxd,atxwebs/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,atxwebs/lxd,atxwebs/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd