block-backend: blk_check_byte_request(): int64_t bytes

block-backend: blk_check_byte_request(): int64_t bytes

Rename size and make it int64_t to correspond to modern block layer,
which always uses int64_t for offset and bytes (not in blk layer yet,
which is a task for following commits).

All callers pass int or unsigned int.

So, for bytes in [0, INT_MAX] nothing is changed, for negative bytes we
now fail on "bytes < 0" check instead of "bytes > INT_MAX" check.

Note, that blk_check_byte_request() still doesn't allow requests
exceeding INT_MAX.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20211006131718.214235-2-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>