Mode transition blocks udev event processing. If user disconnects and
reconnects the cable multiple times during the blockade, usb-moded
will act on stale events that might not reflect the actual state of
the usb connection.

Handle disconnects immediately, but delay acting on connects so that
sequences of multiple disconnects and connects get compressed into
single transition to undefined mode possibly followed by single
transition to appropriated connected mode.
Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>