Add the mapped page count checking flow to avoid invalid page size when
creating MTR.

Fixes: 38389eaa ("RDMA/hns: Add mtr support for mixed multihop addressing")
Link: https://lore.kernel.org/r/1612517974-31867-4-git-send-email-liweihang@huawei.comSigned-off-by: NXi Wang <wangxi11@huawei.com>
Signed-off-by: NWeihang Li <liweihang@huawei.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>