RDMA/core: Avoid redundant memcpy in rdma_addr_find_l2_eth_by_grh

rdma_resolve_ip already copies 'addr' to its dev_addr argument.
Remove the duplicate memcpy and since it was the only user, remove the
'addr' member from resolve_cb_context.

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>