socket.c: Use SO_BINDTODEVICE for ipv6

Signed-off-by: John Newlin <jnewlin@google.com>

--- a/common/socket.c	2014-01-31 11:41:07.000000000 -0800
+++ b/common/socket.c	2014-05-29 08:58:38.939488482 -0700
@@ -236,7 +236,7 @@ if_register_socket(struct interface_info
 
 #if defined(SO_BINDTODEVICE)
 	/* Bind this socket to this interface. */
-	if ((local_family != AF_INET6) && (info->ifp != NULL) &&
+	if ((info->ifp != NULL) &&
 	    setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE,
 			(char *)(info -> ifp), sizeof(*(info -> ifp))) < 0) {
 		log_fatal("setsockopt: SO_BINDTODEVICE: %m");