sw64: fix ip checksum calculation

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I56W9F



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When dest address is not aligned, the checksum result is incorrect. This
is caused by wrong usage of insll and inshl.

Signed-off-by: Cui Mingrui <cuimingrui@wxiat.com>

Signed-off-by: Gu Zitao <guzitao@wxiat.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>