libxl: Normalize MAC address in device conf when hotplugging a netdev

libxl: Normalize MAC address in device conf when hotplugging a netdev

Similar to commits 55ce6564634 and 6c17606b7cc in the qemu driver, make
separate copies of persistent and live device config and normalize the MAC
address between the two. This avoids having different MAC address for the
persistent and live config, ensuring the device has the same address when
the persistent config takes affect after a VM restart.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Laine Stump <laine@redhat.com>