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>