Commit 9f0cb135dd made BUSYBOX_CONFIG_FEATURE_IPV6 dependant on IPV6 but
did not make its default value BUSYBOX_DEFAULT_FEATURE_IPV6 dependant
on IPV6. BUSYBOX_DEFAULT_FEATURE_IPV6 will have as default value y if
IPV6 is enabled otherwise n.
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>