ios: detect switch usermode -> dev mode

this does polling, but only with devices in user mode connected...

Change-Id: I828715a2b4a35f8f9b3bdbcf0da9a74990f3047f
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>