Keep order of decoded flags identical to tcpdump(1)

Improve AccECN packet decoder

This is copied for upstream and includes some other changes
for reducig the diff.

usleep() might be overshooting substantially in that case.

No all variants of FreeBSD this test suite runs on follow the
layout.

Thanks to olivier@freebsd.org for reporting the issue.

Linux uses packed structures for sctp_paddrinfo, sctp_paddrparams,
sctp_prim, and sctp_setpeerprim resulting in not being able to
access some fields directly. Not sure why this is done the way
it is on Linux...

When enabled, no final TCP RST segment or SCTP ABORT chunk is sent
to cleanup the state at the SUT.