usbmuxd: fix tethering not working after iPhone restart

usbmuxd: fix tethering not working after iPhone restart

If the iPhone restarts while the USB cable is still connected,
tethering does not work. This can be fixed by reconnecting.

Fix: if the hotplug.d script detects that carrier is disabled
(no communication), the USB link is reset, and then the
usbmuxd service is restarted. Tethering starts even before
the iPhone is unlocked. As a side effect, if tethering is not
enabled, the iPhone will ding a second time after 5 seconds.

Add dependency on usbutils for usbreset, remove dependency on librt.

[1] https://github.com/libimobiledevice/usbmuxd/issues/218
[2] https://github.com/openwrt/openwrt/issues/12566#issuecomment-2066305622

Signed-off-by: Georgi Valkov <gvalkov@gmail.com>