mlx4: Implement IP based gids support for RoCE/SRIOV

Since there is no connection between the MAC/VLAN and the GID
when using IP-based addressing, the proxy QP1 (running on the
slave) must pass the source-mac, destination-mac, and vlan_id
information separately from the GID. Additionally, the Host
must pass the remote source-mac and vlan_id back to the slave,

This is achieved as follows:
Outgoing MADs:
    1. Source MAC: obtained from the CQ completion structure
       (struct ib_wc, smac field).
    2. Destination MAC: obtained from the tunnel header
    3. vlan_id: obtained from the tunnel header.
Incoming MADs
    1. The source (i.e., remote) MAC and vlan_id are passed in
       the tunnel header to the proxy QP1.

VST mode support:
     For outgoing MADs,  the vlan_id obtained from the header is
        discarded, and the vlan_id specified by the Hypervisor is used
        instead.
     For incoming MADs, the incoming vlan_id (in the wc) is discarded, and the
        "invalid" vlan (0xffff)  is substituted when forwarding to the slave.

Signed-off-by: Moni Shoua <monis@mellanox.co.il>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>