switch_to_random_interface used to do is_connected()
checks and remove interfaces when switching. This
is redundant: interfaces are only added to self.interfaces
once in is_connected() state from process_if_notification().
When they are disconnected, a notification is also received
and process_if_notification() performs the removal. Furthermore,
two other callers of switch_to_interface do not do explicit
is_connected() checks before calling it.