[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>

include/net/sctp/ulpevent.h

@@ -67,7 +67,7 @@ struct sctp_ulpevent {
 };
 
 /* Retrieve the skb this event sits inside of. */
-static inline struct sk_buff *sctp_event2skb(struct sctp_ulpevent *ev)
+static inline struct sk_buff *sctp_event2skb(const struct sctp_ulpevent *ev)
 {
 	return container_of((void *)ev, struct sk_buff, cb);
 }

net/sctp/sm_statefuns.c

@@ -4367,6 +4367,7 @@ sctp_disposition_t sctp_sf_do_prm_asoc(const struct sctp_endpoint *ep,
 				       sctp_cmd_seq_t *commands)
 {
 	struct sctp_chunk *repl;
+	struct sctp_association* my_asoc;
 
 	/* The comment below says that we enter COOKIE-WAIT AFTER
 	 * sending the INIT, but that doesn't actually work in our
@@ -4390,8 +4391,8 @@ sctp_disposition_t sctp_sf_do_prm_asoc(const struct sctp_endpoint *ep,
 	/* Cast away the const modifier, as we want to just
 	 * rerun it through as a sideffect.
 	 */
-	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_ASOC,
-			SCTP_ASOC((struct sctp_association *) asoc));
+	my_asoc = (struct sctp_association *)asoc;
+	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_ASOC, SCTP_ASOC(my_asoc));
 
 	/* Choose transport for INIT. */
 	sctp_add_cmd_sf(commands, SCTP_CMD_INIT_CHOOSE_TRANSPORT,

net/sctp/socket.c

@@ -5868,11 +5868,12 @@ SCTP_STATIC int sctp_msghdr_parse(const struct msghdr *msg,
 				  sctp_cmsgs_t *cmsgs)
 {
 	struct cmsghdr *cmsg;
+	struct msghdr *my_msg = (struct msghdr *)msg;
 
 	for (cmsg = CMSG_FIRSTHDR(msg);
 	     cmsg != NULL;
-	     cmsg = CMSG_NXTHDR((struct msghdr*)msg, cmsg)) {
-		if (!CMSG_OK(msg, cmsg))
+	     cmsg = CMSG_NXTHDR(my_msg, cmsg)) {
+		if (!CMSG_OK(my_msg, cmsg))
 			return -EINVAL;
 
 		/* Should we parse this header or ignore?  */

net/sctp/ulpevent.c

@@ -859,7 +859,7 @@ __u16 sctp_ulpevent_get_notification_type(const struct sctp_ulpevent *event)
 	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;
 }