sctp: declare struct sctp_stream before using it

sctp_stream_free uses struct sctp_stream as a param, but struct sctp_stream
is defined after it's declaration.

This patch is to declare struct sctp_stream before sctp_stream_free.

Fixes: a8386317 ("sctp: prepare asoc stream for stream reconf")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>