MFC r264701:

Send also a packet containing an ABORT chunk in response to an OOTB packet
containing a COOKIE-ECHO chunk.
MFC r264704:

Add consistency checks to ensure that fragments of a user message
have the same U-bit.
MFC r264838:

Don't free an mbuf twice. This only happens in very rare error
cases where the peer sends illegal sequencing information in
DATA chunks for an existing association.
Merge r267482,r267483,r267486,r267577,r267671,r267672 from head:

  Remove send-pr and fix up all references to it.  Replace it with a
  stub send-pr directing people towards the web site.
MFC r265455:

Remove unused code. This is triggered by the bugreport of Sylvestre Ledru
which deal with useless code in the user land stack:
https://bugzilla.mozilla.org/show_bug.cgi?id=1003929
MFC r265691:

For some UDP packets (for example with 200 byte payload) and IP options,
the IP header and the UDP header are not in the same mbuf.
Add code to in_delayed_cksum() to deal with this case.

MFC r265713:

Use KASSERTs as suggested by glebius@
MFC r267105:

Use ENOBUFS instead of ENOMEM in error situations related to m_uiotombuf().
This was suggested by kevlo@.
MFC r267329:

Add support for the SCTP_LOCAL_TRACE_BUF options.
While there, fix some whitespaces.