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.
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.