IB/rxe: Increase max number of completions to 32k

Increase limit of max CQE from 8K to 32K to allow demanding
applications to work over SoftRoCE with same configuration
as most RoCEv2 HW vendors have.

Fixes: 8700e3e7 ("Soft RoCE driver")
Signed-off-by: Yonatan Cohen <yonatanc@mellanox.com>
Reviewed-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>