radvd: show it in config menu when toolchain lacks ipv6

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/radvd/Config.in

@@ -7,3 +7,6 @@ config BR2_PACKAGE_RADVD
 	  IPv6 Router Advertisement Daemon.
 
 	  http://www.litech.org/radvd/
+
+comment "radvd requires a toolchain with IPV6 support"
+	depends on !BR2_INET_IPV6