RDMA/hns: Fix ext_sge num error when post send

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5USIG



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The max_gs is the sum of extended sge and standard sge. In function
fill_ext_sge_inl_data, max_gs does not subtract the number of extended
sges, but is directly used to calculate the size of extended sges.

Signed-off-by: Luoyouming <luoyouming@huawei.com>
Reviewed-by: Yangyang Li <liyangyang20@huawei.com>
Reviewed-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>