thunderbolt: Do not clear USB4 router protocol adapter IFC and ISE bits

These fields are marked as vendor defined in the USB4 spec and should
not be modified by the software, so only clear them when we are dealing
with pre-USB4 hardware.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Yehezkel Bernat <YehezkelShB@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/thunderbolt/path.c

@@ -406,10 +406,17 @@ static int __tb_path_deactivate_hop(struct tb_port *port, int hop_index,
 
 		if (!hop.pending) {
 			if (clear_fc) {
-				/* Clear flow control */
-				hop.ingress_fc = 0;
+				/*
+				 * Clear flow control. Protocol adapters
+				 * IFC and ISE bits are vendor defined
+				 * in the USB4 spec so we clear them
+				 * only for pre-USB4 adapters.
+				 */
+				if (!tb_switch_is_usb4(port->sw)) {
+					hop.ingress_fc = 0;
+					hop.ingress_shared_buffer = 0;
+				}
 				hop.egress_fc = 0;
-				hop.ingress_shared_buffer = 0;
 				hop.egress_shared_buffer = 0;
 
 				return tb_port_write(port, &hop, TB_CFG_HOPS,