Change tap device mac address to prevent change of bridge's mac

Change tap device mac address to prevent change of bridge's mac

Qemu tap device is created with random mac address and then add to
bridge. Due to linux kernel handlig, bridge change its mac address to
tap mac in case tap m ac is lower than bridge one. This can lead to
short network breakage for dom0 a nd guests.

This patch set tap device mac adress to FE:FF:FF:FF:FF:FF to ensure
tap device mac is always higher then bridge one.

(In xen-unstable this is handled by the hotplug scripts, not
qemu-ifup, so the change there is to xen-unstable.hg.)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
Cc: Ian Campbell <Ian.Campbell@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>