Fix "USB tethering" doesn't work after reconnecting USB

Before this CL, if users selects usb tethering option and
reconnects usb it would not start entitlement check.
Because we only start entitlement checks when users select it.

This CL will start entitlement checks when usb tethering option
is selected and reconnects usb.

Bug: 176037347
Test: make -j42 RunSettingsRoboTests
Change-Id: I3a2ad392a1cae9cf97355ef3cd4fb8c23de18673