IB/mlx4: Disable VLAN stripping for RAW PACKET QPs

Fix the asymmetric behavior w.r.t VLAN insertion/stripping for RAW
PACKET QPs -- we don't insert on send and need not strip on receive.

Signed-off-by: Dotan Barak <dotanb@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>