Add a simple passive test.

gtests/net/packetdrill/tests/bsd/sctp/sctp_simple_passive.pkt

++0.0 socket(..., SOCK_STREAM, IPPROTO_SCTP) = 3
+// Check the handshake with en empty(!) cookie
++0.0 bind(3, ..., ...) = 0
++0.0 listen(3, 1) = 0
++0.0 < sctp: INIT[flgs=0, tag=1, a_rwnd=1500, os=1, is=1, tsn=1]
++0.0 > sctp: INIT_ACK[flgs=0, tag=2, a_rwnd=..., os=..., is=..., tsn=1, ...]
++0.1 < sctp: COOKIE_ECHO[flgs=0, len=..., val=...]
++0.0 > sctp: COOKIE_ACK[flgs=0]
++0.0 accept(3, ..., ...) = 4
+// Tear down the association
++1.0 < sctp: SHUTDOWN[flgs=0, cum_tsn=0]
++0.0 > sctp: SHUTDOWN_ACK[flgs=0]
++0.0 < sctp: SHUTDOWN_COMPLETE[flgs=0]
++0.0 close(4) = 0
++0.0 close(3) = 0