zbd: reset one zone at a time

zbd: reset one zone at a time

zbd_rest_zones() currently scans over device zones and try to reset as much
zones as possible at a time. However, this routine takes all the lock on
the range and causes a lot of lock contentions with other threads.

This commit change the behavior to hold the lock and examine one zone at a
time. While it will increase the number of ioctl() call when it need to
reset contiguous, the overhead of increased number of ioctl()s are anyway
amortized by device side's reset performance.

Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>