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/net/ipv6/mip6.c b/net/ipv6/mip6.c
index f61429d..b9779d4 100644
--- a/net/ipv6/mip6.c
+++ b/net/ipv6/mip6.c
@@ -97,16 +97,17 @@
 		return -1;
 
 	if (mh->ip6mh_hdrlen < mip6_mh_len(mh->ip6mh_type)) {
-		LIMIT_NETDEBUG(KERN_DEBUG "mip6: MH message too short: %d vs >=%d\n",
-			       mh->ip6mh_hdrlen, mip6_mh_len(mh->ip6mh_type));
+		net_dbg_ratelimited("mip6: MH message too short: %d vs >=%d\n",
+				    mh->ip6mh_hdrlen,
+				    mip6_mh_len(mh->ip6mh_type));
 		mip6_param_prob(skb, 0, offsetof(struct ip6_mh, ip6mh_hdrlen) +
 				skb_network_header_len(skb));
 		return -1;
 	}
 
 	if (mh->ip6mh_proto != IPPROTO_NONE) {
-		LIMIT_NETDEBUG(KERN_DEBUG "mip6: MH invalid payload proto = %d\n",
-			       mh->ip6mh_proto);
+		net_dbg_ratelimited("mip6: MH invalid payload proto = %d\n",
+				    mh->ip6mh_proto);
 		mip6_param_prob(skb, 0, offsetof(struct ip6_mh, ip6mh_proto) +
 				skb_network_header_len(skb));
 		return -1;
@@ -288,7 +289,7 @@
 			 * XXX: packet if HAO exists.
 			 */
 			if (ipv6_find_tlv(skb, offset, IPV6_TLV_HAO) >= 0) {
-				LIMIT_NETDEBUG(KERN_WARNING "mip6: hao exists already, override\n");
+				net_dbg_ratelimited("mip6: hao exists already, override\n");
 				return offset;
 			}