d/control: record breaks for older qemu-server/pve-container

d/control: record breaks for older qemu-server/pve-container

as we now auto-detect if the 'bridge-disable-mac-learning' is set in
the Network::tap_plug method and disable learning if so, we need to
ensure that the qemu-server and pve-container can cope with that by
manually registering the guests MAC into the FDB.

So this certainly isn't a hard break, but as network is dead for the
guest on update, if that option is set and the new qemu-server and/or
pve-container packages ain't yet updated, it seems still worthy of a
break.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>