veth: create by default nr_possible_cpus queues

This allows easier XDP usage. The number of default active
queues is not changed: 1 RX and 1 TX so that this does
not introduce overhead on the datapath for queue selection.

v1 -> v2:
 - drop the module parameter, force default to nr_possible_cpus - Toke

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>