IB/core: Limit DMAC resolution to RoCE Connected QPs

Resolving DMAC for RoCE is applicable to only Connected mode QPs.
So resolve DMAC for only for Connected mode QPs.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>