Add IPv6 support

[Killeroo]

Can maybe be done by changing port type depending on IP Version ping property (that would need to be added)

[Killeroo]

Would require different socket running ICMPv6, which is already done depending on querried addressed. Forcev6 and Forcev4 both return correct addresses.

http://www.tcpipguide.com/free/t_ICMPCommonMessageFormatandDataEncapsulation.htm
Guide to ICMPv4 and v6 message structure. Both versions have a common message structure which are basically identical, only noticeable difference is type differenced. might require some modfication of orginal ICMP.cs (seems to be reading wrong parts of packet to get type and code info)

May also require new Ping_V6 class?

[Killeroo]

https://notes.shichao.io/tcpv1/ch8/