This is based on https://github.com/freebsd-net/packetdrill/pull/15
but adds support for af_arg, getsockopt() and clearing the
acceptfilter.

Sponsored by:	Netlix, Inc.

copied to the output string. The space required for that extra byte must also be
allocated.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>

add support for sctp_get_assoc_id_lists for [gs]etsockopt, shoult end in an error but didn't do taht for one-to-one socket