sctp: donot reset the overall_error_count in SHUTDOWN_RECEIVE state

Commit f8d96052 ("sctp: Enforce retransmission limit during shutdown")
fixed a problem with excessive retransmissions in the SHUTDOWN_PENDING by not
resetting the association overall_error_count.  This allowed the association
to better enforce assoc.max_retrans limit.

However, the same issue still exists when the association is in SHUTDOWN_RECEIVED
state.  In this state, HB-ACKs will continue to reset the overall_error_count
for the association would extend the lifetime of association unnecessarily.

This patch solves this by resetting the overall_error_count whenever the current
state is small then SCTP_STATE_SHUTDOWN_PENDING.  As a small side-effect, we
end up also handling SCTP_STATE_SHUTDOWN_ACK_SENT and SCTP_STATE_SHUTDOWN_SENT
states, but they are not really impacted because we disable Heartbeats in those
states.

Fixes: Commit f8d96052 ("sctp: Enforce retransmission limit during shutdown")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/sm_sideeffect.c

@@ -702,7 +702,7 @@ static void sctp_cmd_transport_on(sctp_cmd_seq_t *cmds,
 	 * outstanding data and rely on the retransmission limit be reached
 	 * to shutdown the association.
 	 */
-	if (t->asoc->state != SCTP_STATE_SHUTDOWN_PENDING)
+	if (t->asoc->state < SCTP_STATE_SHUTDOWN_PENDING)
 		t->asoc->overall_error_count = 0;
 
 	/* Clear the hb_sent flag to signal that we had a good