net: Convert LIMIT_NETDEBUG to net_dbg_ratelimited

Use the more common dynamic_debug capable net_dbg_ratelimited
and remove the LIMIT_NETDEBUG macro.

All messages are still ratelimited.

Some KERN_<LEVEL> uses are changed to KERN_DEBUG.

This may have some negative impact on messages that were
emitted at KERN_INFO that are not not enabled at all unless
DEBUG is defined or dynamic_debug is enabled.  Even so,
these messages are now _not_ emitted by default.

This also eliminates the use of the net_msg_warn sysctl
"/proc/sys/net/core/warnings".  For backward compatibility,
the sysctl is not removed, but it has no function.  The extern
declaration of net_msg_warn is removed from sock.h and made
static in net/core/sysctl_net_core.c

Miscellanea:

o Update the sysctl documentation
o Remove the embedded uses of pr_fmt
o Coalesce format fragments
o Realign arguments

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/udplite.h b/include/net/udplite.h
index 2caadab..9a28a51 100644
--- a/include/net/udplite.h
+++ b/include/net/udplite.h
@@ -40,7 +40,7 @@
          * checksum. UDP-Lite (like IPv6) mandates checksums, hence packets
          * with a zero checksum field are illegal.                            */
 	if (uh->check == 0) {
-		LIMIT_NETDEBUG(KERN_DEBUG "UDPLite: zeroed checksum field\n");
+		net_dbg_ratelimited("UDPLite: zeroed checksum field\n");
 		return 1;
 	}
 
@@ -52,8 +52,8 @@
 		/*
 		 * Coverage length violates RFC 3828: log and discard silently.
 		 */
-		LIMIT_NETDEBUG(KERN_DEBUG "UDPLite: bad csum coverage %d/%d\n",
-			       cscov, skb->len);
+		net_dbg_ratelimited("UDPLite: bad csum coverage %d/%d\n",
+				    cscov, skb->len);
 		return 1;
 
 	} else if (cscov < skb->len) {