Motivation: NetUtil#isValidIpV6Address and NetUtil#getIPv6ByName allowed an invalid form of mapped IPv4 addresses which lead to accepting invalid IPv6 addresses as valid. Modifications: - NetUtil#isValidIpV6Address and NetUtil#getIPv6ByName should only allow 7 colons for an IPv4 address if they are the first 2 characters. Result: More correct implementation of NetUtil#isValidIpV6Address and NetUtil#getIPv6ByName