block: Limit size to INT_MAX in bdrv_check_byte_request()

Commit 8f4754ed intended to protect against integer overflow bugs in
block drivers by making sure that a single request that is passed to
drivers is no longer than INT_MAX bytes.

However, meanwhile there are some callers that don't use that code path
any more but call bdrv_check_byte_request() directy, so let's add a
check there as well.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
