block: Align max_hw_sectors to logical blocksize

Block device drivers do not have to call blk_queue_max_hw_sectors() to
set a limit on request size if the default limit BLK_SAFE_MAX_SECTORS
is acceptable. However, this limit (255 sectors) may not be aligned
to the device logical block size which cannot be used as is for a
request maximum size. This is the case for the null_blk device driver.

Modify blk_queue_max_hw_sectors() to make sure that the request size
limits specified by the max_hw_sectors and max_sectors queue limits
are always aligned to the device logical block size. Additionally, to
avoid introducing a dependence on the execution order of this function
with blk_queue_logical_block_size(), also modify
blk_queue_logical_block_size() to perform the same alignment when the
logical block size is set after max_hw_sectors.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>