vsprintf: Update %pI6c to not compress a single 0

RFC 5952 (http://tools.ietf.org/html/rfc5952) mandates that 2 or more
consecutive 0's are required before using :: compression.

Update ip6_compressed_string to match the RFC and update the http
reference as well.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/vsprintf.c

@@ -666,6 +666,8 @@ char *ip6_compressed_string(char *p, const char *addr)
 			colonpos = i;
 		}
 	}
+	if (longest == 1)		/* don't compress a single 0 */
+		colonpos = -1;
 
 	/* emit address */
 	for (i = 0; i < range; i++) {
@@ -826,7 +828,7 @@ int kptr_restrict __read_mostly;
  *       IPv4 uses dot-separated decimal with leading 0's (010.123.045.006)
  * - '[Ii]4[hnbl]' IPv4 addresses in host, network, big or little endian order
  * - 'I6c' for IPv6 addresses printed as specified by
- *       http://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-00
+ *       http://tools.ietf.org/html/rfc5952
  * - 'U' For a 16 byte UUID/GUID, it prints the UUID/GUID in the form
  *       "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
  *       Options for %pU are: