Support NAT traversal feature

[matjazv]

What was the problem?

• This PR resolves Implement NAT traversal feature #12.

How was it solved?

• AutoNAT feature is implemented (peer tries to detect if it has public IP or is inside a private network without public IP).
• Circuit-relay feature is implemented (peer offers a circuit relay service to other peers so that peers behind NAT can be called by other peers in the network).
• holepunching feature is implemented (If a peer which calls another peer via its relayer address has a public IP, then called peer drops this connection and directly call peer by its public IP address and they can communicate directly without any relayer peer inbetween. If both peers are behind NAT then holepunching is executed and if it is successfully performed, peers can communicate directly between each other without a relayer peer in between.).

How was it tested?

• New unit tests were implemented.
• Existing and new unit tests passed.

Note

All configuration options have default values from libp2p library. In issue #18 we might change them.

Logs for holepunching feature execution:

• A peer which called another peer via relayer node has a public IP address (no holepunching is needed):

2022-12-14T11:30:45.526+0100    DEBUG   p2p-holepunch   holepunch/svc.go:95     waiting until we have at least one public addresspeer12D3KooWByJ2D6Rv7oe8oUAYTYARiszCAXWUgqkxNp1KbJTqL67E
2022-12-14T11:30:45.776+0100    DEBUG   p2p-holepunch   holepunch/svc.go:107    Host now has a public address. Starting holepunch protocol.
2022-12-14T11:32:07.240+0100    DEBUG   p2p-holepunch   holepunch/holepuncher.go:126    direct connection to peer successful, no need for a hole punch  {"peer": "12D3KooWNfXwDY2xjCF3BJDZniqKRHDZZNQMuVC3gQ1sYzVHvAVx"}

• Both peers are behind NAT so holepunching is needed:

2022-12-14T11:36:31.526+0100    DEBUG   p2p-holepunch   holepunch/svc.go:95     waiting until we have at least one public addresspeer12D3KooWByJ2D6Rv7oe8oUAYTYARiszCAXWUgqkxNp1KbJTqL67E
2022-12-14T11:36:32.776+0100    DEBUG   p2p-holepunch   holepunch/svc.go:107    Host now has a public address. Starting holepunch protocol.
2022-12-14T11:36:33.467+0100    DEBUG   p2p-holepunch   holepunch/holepuncher.go:131    got inbound proxy conn  {"peer": "12D3KooWC9T9yjhAzhjJg48yTosrGxUvTPLm2mtimGZqxeCCdy99"}
2022-12-14T11:36:33.669+0100    DEBUG   p2p-holepunch   holepunch/holepuncher.go:142    peer RTT is 201.757382ms; starting hole punch in 100.878691ms
2022-12-14T11:36:34.066+0100    DEBUG   p2p-holepunch   holepunch/util.go:68    hole punch successful   {"peer": "12D3KooWC9T9yjhAzhjJg48yTosrGxUvTPLm2mtimGZqxeCCdy99"}
2022-12-14T11:36:34.066+0100    DEBUG   p2p-holepunch   holepunch/holepuncher.go:159    hole punching with successful   {"peer": "12D3KooWC9T9yjhAzhjJg48yTosrGxUvTPLm2mtimGZqxeCCdy99", "time": 0.296361071}

[hrmhatef]

Well done.

I just have a small suggestion for one function.