pktcdvd: don't set max_hw_sectors on the underlying device

pktcdvd sets max_hw_sectors on the queue of the underlying device that
it doesn't own (and doesn't reset it ever) since the driver was merged.
This can create all kinds of problems as the underlying driver doesn't
even know about it changing the limit.

As the state purpose is to not create I/Os larger than a single frame,
and pktcdvd never builds bios larger than that, just set REQ_NOMERGE
on the bios it submits so that largers I/Os never get built.

Note: I don't have packet writing hardware, so this is compile tested
only.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240229144408.1047967-1-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>