tor: short circuit host lookup if connecting to IP

With this commit we avoid calling LookupHost if we already have an IPv4
or IPv6 address, as we can return that directly.
This avoids asking Tor to resolve an IPv6 address, which it cannot do.

tor/tor.go

@@ -220,12 +220,20 @@ func ResolveTCPAddr(address, socksAddr string) (*net.TCPAddr, error) {
 		return nil, err
 	}
 
-	ip, err := LookupHost(host, socksAddr)
+	p, err := strconv.Atoi(port)
 	if err != nil {
 		return nil, err
 	}
 
-	p, err := strconv.Atoi(port)
+	// Do we already have an IP? Then we don't need to look up anything.
+	if ip := net.ParseIP(host); ip != nil {
+		return &net.TCPAddr{
+			IP:   ip,
+			Port: p,
+		}, nil
+	}
+
+	ip, err := LookupHost(host, socksAddr)
 	if err != nil {
 		return nil, err
 	}