Revert "sctp: Fix SHUTDOWN CTSN Ack in the peer restart case"

This reverts commit 12dfd78e.

This can be reverted as shutdown and cookie_ack chunk are using the
same asoc since commit 35b4f244 ("sctp: do asoc update earlier
in sctp_sf_do_dupcook_a").
Reported-by: Jere Leppänen <jere.leppanen@nokia.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/sm_make_chunk.c

@@ -858,11 +858,7 @@ struct sctp_chunk *sctp_make_shutdown(const struct sctp_association *asoc,
 	struct sctp_chunk *retval;
 	__u32 ctsn;
 
-	if (chunk && chunk->asoc)
-		ctsn = sctp_tsnmap_get_ctsn(&chunk->asoc->peer.tsn_map);
-	else
-		ctsn = sctp_tsnmap_get_ctsn(&asoc->peer.tsn_map);
-
+	ctsn = sctp_tsnmap_get_ctsn(&asoc->peer.tsn_map);
 	shut.cum_tsn_ack = htonl(ctsn);
 
 	retval = sctp_make_control(asoc, SCTP_CID_SHUTDOWN, 0,