Revert https://svnweb.freebsd.org/changeset/base/357829

This introduces a regression reported by koobs@ when running a pyhton
test suite on a loaded system.

This patch resulted in a failing accept() call, when the association
was setup and gracefully shutdown by the peer before accept was called.
So the following packetdrill script would fail:

+0.0 socket(..., SOCK_STREAM, IPPROTO_SCTP) = 3
+0.0 bind(3, ..., ...) = 0
+0.0 listen(3, 1) = 0
+0.0 < sctp: INIT[flgs=0, tag=1, a_rwnd=15000, 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 < sctp: DATA[flgs=BE, len=116, tsn=1, sid=0, ssn=0, ppid=0]
+0.0 > sctp: SACK[flgs=0, cum_tsn=1, a_rwnd=..., gaps=[], dups=[]]
+0.0 < sctp: SHUTDOWN[flgs=0, cum_tsn=0]
+0.0 > sctp: SHUTDOWN_ACK[flgs=0]
+0.0 < sctp: SHUTDOWN_COMPLETE[flgs=0]
+0.0 accept(3, ..., ...) = 4
+0.0 close(3) = 0
+0.0 recv(4, ..., 4096, 0) = 100
+0.0 recv(4, ..., 4096, 0) = 0
+0.0 close(4) = 0

Reported by: koops@