This fixes a subtle bug, the WQ mailbox has only 5 bits to describe the
page_offset, while mlx5_ib_get_buf_offset() is hard wired to only work
with 6 bit page_offsets.

Thus it did not properly reject badly aligned buffers.

Fixes: 79b20a6c ("IB/mlx5: Add receive Work Queue verbs")
Fixes: 0fb2ed66 ("IB/mlx5: Add create and destroy functionality for Raw Packet QP")
Link: https://lore.kernel.org/r/20201115114311.136250-3-leon@kernel.orgSigned-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>