RDMA/hns: Optimize WQE buffer size calculating process

Optimize the QP's WQE buffer parameters calculating process to make the
codes more readable mainly by merging calculation of extended sge space of
kernel and userspace. In addition, add some inline functions to simply
codes about multi-hop addressing.

Link: https://lore.kernel.org/r/1588071823-40200-4-git-send-email-liweihang@huawei.com
Signed-off-by: Xi Wang <wangxi11@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>