thunderbolt: Scan only valid NULL adapter ports in hotplug

The only way to expand Thunderbolt topology is through the NULL adapter
ports (typically ports 1, 2, 3 and 4). There is no point handling
Thunderbolt hotplug events on any other port.

Add a helper function (tb_port_is_null()) that can be used to determine
if the port is NULL port, and use it in software connection manager code
when hotplug event is handled.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/tb.c

@@ -356,11 +356,13 @@ static void tb_handle_hotplug(struct work_struct *work)
 		tb_port_info(port,
 			     "got plug event for connected port, ignoring\n");
 	} else {
+		if (tb_port_is_null(port)) {
 			tb_port_info(port, "hotplug: scanning\n");
 			tb_scan_port(port);
 			if (!port->remote)
 				tb_port_info(port, "hotplug: no switch found\n");
 		}
+	}
 
 put_sw:
 	tb_switch_put(sw);

drivers/thunderbolt/tb.h

@@ -350,6 +350,11 @@ static inline bool tb_port_has_remote(const struct tb_port *port)
 	return true;
 }
 
+static inline bool tb_port_is_null(const struct tb_port *port)
+{
+	return port && port->port && port->config.type == TB_TYPE_PORT;
+}
+
 static inline bool tb_port_is_pcie_down(const struct tb_port *port)
 {
 	return port && port->config.type == TB_TYPE_PCIE_DOWN;