sw64: fix __csum_and_copy when dest is not 8-byte aligned

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



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When destination is not 8-byte aligned,
csum_partial_cfu_dest_unaligned() should be used to avoid kernel
unaligned exception.

Fixes: 2fcadd2861b4 ("sw64: optimize ip checksum calculation")
Signed-off-by: Mao Minkai <maominkai@wxiat.com>

Signed-off-by: Gu Zitao <guzitao@wxiat.com>