blktrace: change the internal action to 64bit

blktrace: change the internal action to 64bit

Change the internal use of the action in blktrace to 64bit. Although for
now only the lower 32bits will be used.

With the upcoming version 2 of the blktrace user-space protocol the upper
32bit will also be utilized.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>