tirex: support enqueue req in background

Signed-off-by: Hiroshi Miura <miurahr@linux.com>
tirex: add priority handling

Signed-off-by: Hiroshi Miura <miurahr@linux.com>
tirex: change api

Signed-off-by: Hiroshi Miura <miurahr@linux.com>
tirex: fix get_handle error

Signed-off-by: Hiroshi Miura <miurahr@linux.com>
tirex: fix bk requests errors

- missing variable defintions
- add special state for background coroutine
- fix stupid typo

Signed-off-by: Hiroshi Miura <miurahr@linux.com>
Merge pull request #3 from miurahr/bk-enqueue

New API and feature to add background  enqueue requests.