multi: Added a NetInterface to clean up config.go

This commit adds a new interface named NetInterface and two
implementations of it: RegularNet & TorProxyNet. These two structs
are used in config.go in an attempt to clean up the code and
abstract away the dialer and DNS functions.

brontide/conn.go

@@ -38,11 +38,10 @@ func Dial(localPriv *btcec.PrivateKey, netAddr *lnwire.NetAddress,
 	var conn net.Conn
 	var err error
 	if dialer == nil {
-		// A Tor proxy dial function WAS NOT passed in.
+		// A dial function WAS NOT passed in.
 		conn, err = net.Dial("tcp", ipAddr)
 	} else {
-		// A Tor proxy dial function WAS passed in so we use it instead
-		// of golang's net.Dial.
+		// A dial function WAS passed in so we use it instead.
 		conn, err = dialer[0]("tcp", ipAddr)
 	}
 	if err != nil {