net: ipv6: Standardize prefixes for message logging

Add #define pr_fmt(fmt) as appropriate.

Add "IPv6: " to appropriate files.

Convert printk(KERN_<LEVEL> to pr_<level> (but not KERN_DEBUG).
Standardize on "%s: " not "%s(): " when emitting __func__.
Use "%s: ", __func__ instead of embedding function name.
Coalesce formats, align arguments.

ADDRCONF output is now prefixed with "IPv6: "

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 7dfb89f..2a3a22c 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -2627,8 +2627,7 @@
 	err = inet_ctl_sock_create(&net->ipv6.igmp_sk, PF_INET6,
 				   SOCK_RAW, IPPROTO_ICMPV6, net);
 	if (err < 0) {
-		printk(KERN_ERR
-		       "Failed to initialize the IGMP6 control socket (err %d).\n",
+		pr_err("Failed to initialize the IGMP6 control socket (err %d)\n",
 		       err);
 		goto out;
 	}