This allows userland to set a possibly different link-local address
like say one based on RFC7217.

Signed-off-by: Roy Marples <roy@marples.name>

--- net/ipv6/addrconf.c.orig	2014-08-10 19:39:50.377073417 +0000
+++ net/ipv6/addrconf.c	2014-08-10 20:19:03.139002051 +0000
@@ -2751,6 +2751,11 @@ static void addrconf_dev_config(struct n
 	if (IS_ERR(idev))
 		return;
 
+	/* If we already have a link-local address, don't bother
+	 * adding a new one. */
+	if (ipv6_get_lladdr(dev, &addr, 0) == 0)
+		return;
+
 	memset(&addr, 0, sizeof(struct in6_addr));
 	addr.s6_addr32[0] = htonl(0xFE800000);