RDMA/rxe: Add rxe_srq_cleanup()

Move cleanup code from rxe_destroy_srq() to rxe_srq_cleanup() which is
called after all references are dropped to allow code depending on the srq
object to complete.

Link: https://lore.kernel.org/r/20220421014042.26985-3-rpearsonhpe@gmail.com


Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>