recreated seeds by selecting peers across 20+ nodes that:
1. Keep up with updates, in this case run 1.14.3 or higher
2. Have NODE_NETWORK set
3. Are not known scanning clients
4. Are connectable
5. Are stable - I ordered nodes by time they have been connected to
one of my nodes
resulting set is 120 good nodes for mainnet and 20 good nodes for
testnet, serialized into chainparamsseeds.h using the contrib/
scripts.
This makes it possible for a node with `-onlynet=tor` to bootstrap
itself.
It also adds the base infrastructure for adding IPv6 seed nodes.
Also represent IPv4 fixed seed addresses in 16-byte format.