* Add luci.ip.cidr.is6mapped4() to test whether an IPv6 CIDR is a mapped IPv4 one
* Add luci.ip.cidr.mapped4() to derive IPv4 from mapped CIDR
* Remove mapped IPv4 workaround from constructor as it breaks genuine addrs like ::ffff:0
Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>