RDMA/rxe: Replace include statement

rxe_queue.h currently includes <uapi/rdma/rdma_user_rxe.h> for a
definition of struct rxe_queue_buf. But it is only used as a pointer so
the definition is not needed.

This patch replaces the include statement with the declaration

     struct rxe_queue_buf;

Link: https://lore.kernel.org/r/20220630190425.2251-5-rpearsonhpe@gmail.com


Reported-by: Frank Zago <frank.zago@hpe.com>
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>