nvme: default to 0 poll queues

We need a better way of configuring this, and given that polling is
(still) a bit niche, let's default to using 0 poll queues. That way
we'll have the same read/write/poll behavior as 4.20, and users that
want to test/use polling are required to do manual configuration of the
number of poll queues.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/nvme/host/pci.c

@@ -86,7 +86,7 @@ MODULE_PARM_DESC(write_queues,
 	"Number of queues to use for writes. If not set, reads and writes "
 	"will share a queue set.");
 
-static int poll_queues = 1;
+static int poll_queues = 0;
 module_param_cb(poll_queues, &queue_count_ops, &poll_queues, 0644);
 MODULE_PARM_DESC(poll_queues, "Number of queues to use for polled IO.");