net: remove the xps possible_mask

Remove the xps possible_mask. It was an optimization but we can just
loop from 0 to nr_ids now that it is embedded in the xps dev_maps. That
simplifies the code a bit.

Suggested-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>