quagga: ripngd support needs ipv6 support in toolchain

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/quagga/Config.in

@@ -25,6 +25,7 @@ config BR2_PACKAGE_QUAGGA_RIPD
 
 config BR2_PACKAGE_QUAGGA_RIPNGD
 	bool "ripngd support"
+	depends on BR2_INET_IPV6
 	help
 	  Enable ripngd support in quagga.