sctp: define SCTP_SS_DEFAULT for Stream schedulers

According to rfc8260#section-4.3.2, SCTP_SS_DEFAULT is required to
defined as SCTP_SS_FCFS or SCTP_SS_RR.

SCTP_SS_FCFS is used for SCTP_SS_DEFAULT's value in this patch.

Fixes: 5bbbbe32 ("sctp: introduce stream scheduler foundations")
Reported-by: NJianwen Ji <jiji@redhat.com>
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/uapi/linux/sctp.h

@@ -1153,6 +1153,7 @@ struct sctp_add_streams {
 /* SCTP Stream schedulers */
 enum sctp_sched_type {
 	SCTP_SS_FCFS,
+	SCTP_SS_DEFAULT = SCTP_SS_FCFS,
 	SCTP_SS_PRIO,
 	SCTP_SS_RR,
 	SCTP_SS_MAX = SCTP_SS_RR

net/sctp/outqueue.c

@@ -212,7 +212,7 @@ void sctp_outq_init(struct sctp_association *asoc, struct sctp_outq *q)
 	INIT_LIST_HEAD(&q->retransmit);
 	INIT_LIST_HEAD(&q->sacked);
 	INIT_LIST_HEAD(&q->abandoned);
-	sctp_sched_set_sched(asoc, SCTP_SS_FCFS);
+	sctp_sched_set_sched(asoc, SCTP_SS_DEFAULT);
 }
 
 /* Free the outqueue structure and any related pending chunks.