These days, DEV_OPEN calls to character drivers block the calling
thread until completion or failure, and thus never return SUSPEND to
the caller. The same already applied to BDEV_OPEN calls to block
drivers. It has thus become impossible for a process to enter a state
of being blocked on a device open call.
There is currently no support for restarting device open calls to
restarted character drivers. This support was present in the _DOPEN
logic, but was already no longer triggering. In the future, this case
should be handled by the thread performing the open request.