RDMA/hns: Limit extend sq sge num

According to hip08 limit, the buffer size of extend sge needs to be an
integer wqe_sge_buf_page size. For example, the value of sge_shift field
of qp context is greater or equal to eight when buffer page size is 4K
size. The value of sge_shift field of qp context assigned by
hr_qp->sge.sge_cnt.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>