net: ixgbe: use skb_csum_is_sctp instead of protocol check

mainline inclusion
from mainline-v5.12-rc1-dontuse
commit f8c4b01d
category: feature
bugzilla: 173966
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f8c4b01d3a680de2144dd274df03ffaf69cfb881



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Using skb_csum_is_sctp is a easier way to validate it's a SCTP CRC
checksum offload packet, and yet it also makes ixgbe support SCTP
CRC checksum offload for UDP and GRE encapped packets, just as it
does in igb driver.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Yongxin Li <liyongxin1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>