Merge branch 'socketoption_sctp_initmsg_with_expressions' of https://github.com/hoelscher/packetdrill into hoelscher-socketoption_sctp_initmsg_with_expressions

While there, fix some whitespace issues.

Linux uses in some cases only enums, so one can't check with #ifdef.

For now don't allocate memory, so we don't have to free it.
This will not work for all future socket options, but it simplifies
things for now.

Merge I-DATA support.

This fixes #25, #27, and #29.