p2p/discover: new endpoint format

This commit changes the discovery protocol to use the new "v4" endpoint
format, which allows for separate UDP and TCP ports and makes it
possible to discover the UDP address after NAT.

p2p/discover/table_test.go

@@ -261,9 +261,9 @@ func (t findnodeOracle) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID
 		panic("query to node at distance 0")
 	default:
 		// TODO: add more randomness to distances
-		next := toaddr.Port - 1
+		next := uint16(toaddr.Port) - 1
 		for i := 0; i < bucketSize; i++ {
-			result = append(result, &Node{ID: randomID(t.target, next), DiscPort: next})
+			result = append(result, &Node{ID: randomID(t.target, int(next)), UDP: next})
 		}
 	}
 	return result, nil