Check if there is ipv4 or tor addresses embedded in ipv6 is missing for `netaddressv2`

[brunoerg]

When reading a netaddressv2, btcd doesn't check if there is an ipv4 embedded into an ipv6 address, this might be ok for v1 encoding but not for v2. This kind of address, for example, is ignored by Core and pointed out as invalid.

For reference: https://github.com/brunoerg/bitcoinfuzz/issues/49