Add a new packet type for an extended listreq and listresp

The current LISTRESP packet has the following anatomy:
4 bytes ( packet type )
4 bytes ( total servers listed )
4 bytes ( packed servers )
4x bytes ( where an ipv4 IP is stored as 4 quads )
Up to a maximum of 570 bytes total.

Unfortunately 4 bytes is not enough to transmit an IPV6 address.

An additional LISTRESPEXT packet will need to be created and will have the following anatomy:
4 bytes ( packet type )
4 bytes ( total servers listed )
4 bytes ( packed servers )
16x bytes ( 128 bits required for an ipv6 address, stored as the 4x4 hex tuples )

In tandem, a LISTREQEXT will need to be created, with the same anatomy of a LISTREQ.