Fix a bug in INIT handling on accepted 1-to-1 style sockets when the
listener is closed.
This fix allows the following packetdrill test to pass:
Setup a connected, blocking 1-to-1 style socket
+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, ...]
+0.0 < sctp: COOKIE_ECHO[flgs=0, len=..., val=...]
+0.0 > sctp: COOKIE_ACK[flgs=0]
+0.0 accept(3, ..., ...) = 4
+0.0 close(3) = 0
// Inject an INIT chunk and expect an INIT-ACK
+0.0 < sctp: INIT[flgs=0, tag=3, a_rwnd=1500, os=1, is=1, tsn=1]
+0.0 > sctp: INIT_ACK[flgs=0, tag=..., a_rwnd=..., os=..., is=..., tsn=..., ...]

MFC after: 3 days