preseed_base, ts-host-install: Change NIC NamePolicy to "mac"

preseed_base, ts-host-install: Change NIC NamePolicy to "mac"

On "italia?" machine, the two network interfaces are competing to have
"eno1", base on the "onboard" naming policy. So the name of the
network interface can change between "eno1" and "eth0".

Switching to "mac" should avoid the unpredictable name based on
"onboard" or "slot" policy.

The "mac" naming policy break `vif-bridge` for the "vif*.*" network
interfaces. So we will avoid the "mac" policy if the driver is "vif".
This also have an impact on guest created with ./ts-debian-install, as
they use the initrd from dom0, so the interface in the guest will be
renamed according to default policy (which rename eth0 to enX0).

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>