net: hns3: replace skb->csum_not_inet with skb_csum_is_sctp

Commit fa821170 ("net: add inline function skb_csum_is_sctp")
missed replacing skb->csum_not_inet check in hns3. This patch is
to replace it with skb_csum_is_sctp().

Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/r/3ad3c22c08beb0947f5978e790bd98d2aa063df9.1611307861.git.lucien.xin@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>