Revert "sctp: Fix bundling of SHUTDOWN with COOKIE-ACK"

This can be reverted as shutdown and cookie_ack chunk are using the
same asoc since the last patch.

This reverts commit 145cb2f7

.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>