[SCTP]: Fix compiler warning about const qualifiers

Fix 3 warnings about discarding const qualifiers:

net/sctp/ulpevent.c:862: warning: passing argument 1 of 'sctp_event2skb' discards qualifiers from pointer target type
net/sctp/sm_statefuns.c:4393: warning: passing argument 1 of 'SCTP_ASOC' discards qualifiers from pointer target type
net/sctp/socket.c:5874: warning: passing argument 1 of 'cmsg_nxthdr' discards qualifiers from pointer target type

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
index b43f1f1..ce6cda6 100644
--- a/net/sctp/ulpevent.c
+++ b/net/sctp/ulpevent.c
@@ -859,7 +859,7 @@
 	union sctp_notification *notification;
 	struct sk_buff *skb;
 
-	skb = sctp_event2skb((struct sctp_ulpevent *)event);
+	skb = sctp_event2skb(event);
 	notification = (union sctp_notification *) skb->data;
 	return notification->sn_header.sn_type;
 }