sctp: handle ootb packet in chunk order as defined

Changed the order of processing SHUTDOWN ACK and COOKIE ACK
refer to section 8.4:Handle "Out of the Blue" Packets.

SHUTDOWN ACK chunk should be processed before processing
"Stale Cookie" ERROR or a COOKIE ACK.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Shan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>