Add support for per-file/inode stream ID

Add support for per-file/inode stream ID

Writing on flash devices can be much more efficient, if we can
inform the device what kind of data can be grouped together. If
the device is able to group data together with similar lifetimes,
then it can be more efficient in garbage collection. This, in turn,
leads to lower write amplification, which is a win on both device
wear and performance.

Signed-off-by: Jens Axboe <axboe@fb.com>