[IPV6]: Include ipv6.h for ipv6_addr_set

This patch includes net/ipv6.h from addrconf.h since it needs
ipv6_addr_set.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/addrconf.h

@@ -46,6 +46,7 @@ struct prefix_info {
 #include <linux/in6.h>
 #include <linux/netdevice.h>
 #include <net/if_inet6.h>
+#include <net/ipv6.h>
 
 #define IN6_ADDR_HSIZE		16