block: soft limit zone-append sectors as well

Martin rightfully noted that for normal filesystem IO we have soft limits
in place, to prevent them from getting too big and not lead to
unpredictable latencies. For zone append we only have the hardware limit
in place.

Cap the max sectors we submit via zone-append to the maximal number of
sectors if the second limit is lower.

Reported-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/linux-btrfs/yq1k0w8g3rw.fsf@ca-mkp.ca.oracle.com


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