IB/mlx4: Set link type for RAW PACKET QPs in the QP context

When the link type is Ethernet, setting the link type in the QP
context will enable TCP/IP stateless offloads (checksum, LSO, RSS) for
RAW PACKET Ethernet QPs.  For IB UD QPs this worked OK since the value
assumed by the firmware for IB link layer is zero.

Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>