In order to conform to other drivers stop using rkey == 0 as an indication
that there are no remote access flags set.  Set rkey == lkey by default
for all MRs.

Link: https://lore.kernel.org/r/20230530221334.89432-6-rpearsonhpe@gmail.comSigned-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>