sctp: implement event notification SCTP_SENDER_DRY_EVENT

This patch implement event notification SCTP_SENDER_DRY_EVENT.
SCTP Socket API Extensions:

  6.1.9. SCTP_SENDER_DRY_EVENT

  When the SCTP stack has no more user data to send or retransmit, this
  notification is given to the user. Also, at the time when a user app
  subscribes to this event, if there is no data to be sent or
  retransmit, the stack will immediately send up this notification.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sctp/sm.h b/include/net/sctp/sm.h
index 652f09b..9148632 100644
--- a/include/net/sctp/sm.h
+++ b/include/net/sctp/sm.h
@@ -165,6 +165,7 @@
 sctp_state_fn_t sctp_sf_do_prm_asconf;
 
 /* Prototypes for other event state functions.  */
+sctp_state_fn_t sctp_sf_do_no_pending_tsn;
 sctp_state_fn_t sctp_sf_do_9_2_start_shutdown;
 sctp_state_fn_t sctp_sf_do_9_2_shutdown_ack;
 sctp_state_fn_t sctp_sf_ignore_other;