This fixes https://github.com/nplab/packetdrill/issues/5.

This patch add support for the PAD chunk and PAD parameter defined
in https://tools.ietf.org/html/rfc4820
This fixes https://github.com/nplab/packetdrill/issues/16

This patch adds support for the SCTP parameters defined in RFC 4960.
While there, make the syntax more consistent and make sure that
the packet printing is in line with the syntax being used.
This fixes https://github.com/nplab/packetdrill/issues/6

Put in a missing ',' between the flags and error causes when
printing ABORT[] and ERROR[] chunks if both are available.

This commit adds support for parsing SCTP packets and converting them
to strings. Currently only chunks, parameters and error causes specified
in RFC 4960 are supported. Support for other RFCs will be added in the
future.
Tested on FreeBSD (amd64 and arm) and Linux.

Signed-off-by: Michael Tuexen <tuexen@fh-muenster.de>