RDMA/rxe: Skip dgid check in loopback mode

RDMA/rxe: Skip dgid check in loopback mode

In the loopback tests, the following call trace occurs.

 Call Trace:
  __rxe_do_task+0x1a/0x30 [rdma_rxe]
  rxe_qp_destroy+0x61/0xa0 [rdma_rxe]
  rxe_destroy_qp+0x20/0x60 [rdma_rxe]
  ib_destroy_qp_user+0xcc/0x220 [ib_core]
  uverbs_free_qp+0x3c/0xc0 [ib_uverbs]
  destroy_hw_idr_uobject+0x24/0x70 [ib_uverbs]
  uverbs_destroy_uobject+0x43/0x1b0 [ib_uverbs]
  uobj_destroy+0x41/0x70 [ib_uverbs]
  __uobj_get_destroy+0x39/0x70 [ib_uverbs]
  ib_uverbs_destroy_qp+0x88/0xc0 [ib_uverbs]
  ib_uverbs_handler_UVERBS_METHOD_INVOKE_WRITE+0xb9/0xf0 [ib_uverbs]
  ib_uverbs_cmd_verbs+0xb16/0xc30 [ib_uverbs]

The root cause is that the actual RDMA connection is not created in the
loopback tests and the rxe_match_dgid will fail randomly.

To fix this call trace which appear in the loopback tests, skip check of
the dgid.

Fixes: 5deaf88696f1 ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20200630123605.446959-1-leon@kernel.org
Signed-off-by: Zhu Yanjun <yanjunz@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>