sctp: fix strchange_flags name for Stream Change Event

As defined in rfc6525#section-6.1.3, SCTP_STREAM_CHANGE_DENIED
and SCTP_STREAM_CHANGE_FAILED should be used instead of
SCTP_ASSOC_CHANGE_DENIED and SCTP_ASSOC_CHANGE_FAILED.

To keep the compatibility, fix it by adding two macros.

Fixes: b444153f ("sctp: add support for generating add stream change event notification")
Reported-by: Jianwen Ji <jiji@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>