[IPV6]: fix ipv6_saddr_score struct element

The scope element in the ipv6_saddr_score struct used in 
ipv6_dev_get_saddr() is an unsigned integer, but __ipv6_addr_src_scope() 
returns a signed integer (and can return -1).
Signed-off-by: NBrian Haley <brian.haley@hp.com>
Acked-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -822,7 +822,7 @@ struct ipv6_saddr_score {
 	int		addr_type;
 	unsigned int	attrs;
 	int		matchlen;
-	unsigned int	scope;
+	int		scope;
 	unsigned int	rule;
 };