Exit accessory mode more aggressively

The debouncing of USB disconnects means that the disconnect caused
by resetting the connection without unplugging the device does not make
it to the handler, and thus doesn't exit accessory mode. Therefore we
must exit accessory mode even for connect events after we have left the
entering accessory mode state.

Test: Manual testing with desktop head unit
Change-Id: Ia028ff28783fa777a9f8bcd86b523d01f633a140