thunderbolt: Do not program NFC buffers for USB4 router protocol adapters

USB4 spec says that NFC buffers field is not used for protocol adapters,
only for lane adapters so make tb_port_add_nfc_credits() skip non-lane
adapters in order to follow the spec.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/switch.c

@@ -601,6 +601,13 @@ int tb_port_add_nfc_credits(struct tb_port *port, int credits)
 	if (credits == 0 || port->sw->is_unplugged)
 		return 0;
 
+	/*
+	 * USB4 restricts programming NFC buffers to lane adapters only
+	 * so skip other ports.
+	 */
+	if (tb_switch_is_usb4(port->sw) && !tb_port_is_null(port))
+		return 0;
+
 	nfc_credits = port->config.nfc_credits & ADP_CS_4_NFC_BUFFERS_MASK;
 	nfc_credits += credits;