Fix zero dmac race in neighbor resolution

Cc: linux-rdma@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
To: Jason Gunthorpe <jgg@ziepe.ca>
To: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>

--- b4-submit-tracking ---
# This section is used internally by b4 prep for tracking purposes.
{
  "series": {
    "revision": 1,
    "change-id": "20260405-fix-dmac-race-1c57aa966d4d",
    "prefixes": [
      "rdma-next"
    ],
    "presubject": ""
  }
}