[client] Fix ipv6 address in quic server (#5763)

* [client] Use `net.JoinHostPort` for consistency in constructing host-port pairs

* [client] Fix handling of IPv6 addresses by trimming brackets in `net.JoinHostPort`

Author: pappz

shared/relay/client/dialer/quic/quic.go

@@ -89,12 +89,12 @@ func prepareURL(address string) (string, error) {
 	finalHost, finalPort, err := net.SplitHostPort(host)
 	if err != nil {
 		if strings.Contains(err.Error(), "missing port") {
-			return host + ":" + defaultPort, nil
+			return net.JoinHostPort(strings.Trim(host, "[]"), defaultPort), nil
 		}
 
 		// return any other split error as is
 		return "", err
 	}
 
-	return finalHost + ":" + finalPort, nil
+	return net.JoinHostPort(finalHost, finalPort), nil
 }