net/mlx5e: Allow MAC invalidation while spoofchk is ON

Prior to this patch the driver prohibited spoof checking on invalid MAC.
Now the user can set this configuration if it wishes to.

This is required since libvirt might invalidate the VF Mac by setting it
to zero, while spoofcheck is ON.

Fixes: 1ab2068a ("net/mlx5: Implement vports admin state backup/restore")
Signed-off-by: Aya Levin <ayal@mellanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>