RDMA/ocrdma: Resolve L2 address when creating user AH

Because of IP-based GIDs, userspace AHs must have MAC and VLAN ID
resolved separately.  Presently, user AHs are broken for ocrdma.  This
patch resolves L2 addresses while creating user AH and obtains the
right DMAC and VLAN ID before creating AH.

Signed-off-by: Devesh Sharma <devesh.sharma@emulex.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>