MFC r263094:

SCTP uses CRC32C and not Adler anymore. While there change the reference
to RFC 4960.
This does not change any code, just comments.
MFC r263096:

Put the offset of the CRC32C in csum_data instead of 0.
The virtio driver needs the offset to be stored in csum_data,
like in the case for UDP and TCP.

The virtio problem was reported by
Niu Zhixiong <kaiaixi@gmail.com>, who helped in debugging
and testing the patch.