net: sctp: stop spamming klog with rfc6458, 5.3.2. deprecation warnings

Back then when we added support for SCTP_SNDINFO/SCTP_RCVINFO from
RFC6458 5.3.4/5.3.5, we decided to add a deprecation warning for the
(as per RFC deprecated) SCTP_SNDRCV via commit bbbea41d ("net:
sctp: deprecate rfc6458, 5.3.2. SCTP_SNDRCV support"), see [1].

Imho, it was not a good idea, and we should just revert that message
for a couple of reasons:

  1) It's uapi and therefore set in stone forever.

  2) To be able to run on older and newer kernels, an SCTP application
     would need to probe for both, SCTP_SNDRCV, but also SCTP_SNDINFO/
     SCTP_RCVINFO support, so that on older kernels, it can make use
     of SCTP_SNDRCV, and on newer kernels SCTP_SNDINFO/SCTP_RCVINFO.
     In my (limited) experience, a lot of SCTP appliances are migrating
     to newer kernels only ve(ee)ry slowly.

  3) Some people don't have the chance to change their applications,
     f.e. due to proprietary legacy stuff. So, they'll hit this warning
     in fast path and are stuck with older kernels.

But i.e. due to point 1) I really fail to see the benefit of a warning.
So just revert that for now, the issue was reported up Jamal.

  [1] http://thread.gmane.org/gmane.linux.network/321960/Reported-by: NJamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Cc: Michael Tuexen <tuexen@fh-muenster.de>
Acked-by: NJamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/socket.c

@@ -2200,12 +2200,6 @@ static int sctp_setsockopt_events(struct sock *sk, char __user *optval,
 	if (copy_from_user(&sctp_sk(sk)->subscribe, optval, optlen))
 		return -EFAULT;
 
-	if (sctp_sk(sk)->subscribe.sctp_data_io_event)
-		pr_warn_ratelimited(DEPRECATED "%s (pid %d) "
-				    "Requested SCTP_SNDRCVINFO event.\n"
-				    "Use SCTP_RCVINFO through SCTP_RECVRCVINFO option instead.\n",
-				    current->comm, task_pid_nr(current));
-
 	/* At the time when a user app subscribes to SCTP_SENDER_DRY_EVENT,
 	 * if there is no data to be sent or retransmit, the stack will
 	 * immediately send up this notification.