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.
MFC r263237:

* Provide information in error causes in ASCII instead of
  proprietary binary format.
* Add support for a diagnostic information error cause.
  The code is sysctlable and the default is 0, which
  means it is not sent.

This is joint work with rrs@.
MFC r263921:

Use SCTP_OVER_UDP_TUNNELING_PORT more consistently.
MFC r263922:

Handle an edge case of address management similar to TCP.
This needs to be reconsidered when the address handling
will be reimplemented.
The patch is from rrs@.
MFC r264017:

Increment the SSN only after processing the last fragment of an
ordered user message.
MFC r264241:

Call sctp_addr_change() from rt_addrmsg() instead of rt_newaddrmsg_fib(),
since rt_addrmsg() gets also called from other functions.
MFC r264679:

Send the correct error cause, when a DATA chunk with no user data
is received. This bug was reported by Irene Ruengeler.
MFC r264682:

Use consistently debug output instead of an unconditional printf.