bramble: usb: add state of usb extcon to monitorffs am: 8fd66e78c8

Original change: https://android-review.googlesource.com/c/device/google/bramble/+/1686047

Change-Id: Ifd83c95096aa839597a5f86ddb5c7f84819b3979
diff --git a/usb/UsbGadget.h b/usb/UsbGadget.h
index 93c7d66..32b173f 100644
--- a/usb/UsbGadget.h
+++ b/usb/UsbGadget.h
@@ -66,7 +66,8 @@
 using ::std::string;
 
 constexpr char kGadgetName[] = "a600000.dwc3";
-static MonitorFfs monitorFfs(kGadgetName);
+constexpr char kExtconUsbState[] = "/sys/class/extcon/extcon4/cable.0/state";
+static MonitorFfs monitorFfs(kGadgetName, kExtconUsbState);
 
 struct UsbGadget : public IUsbGadget {
     UsbGadget();