IB/mlx4: Add port aggregation support

Register the interface with the mlx4 core driver with port aggregation support
and check for port aggregation mode when the 'add' function is called.

In this mode, only one physical port is reported to the upper layer
(RoCE/IB core stack and ULPs).

Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>