alsa-gobject: add API to get current protocol version in each interface

alsa-project/alsa-gobject pull request #44 was opened from takaswie:

In UAPI of Linux sound subsystem, interfaces support protocol versioning. This patchset adds API to get current protocol version in each interface.

Request URL : https://github.com/alsa-project/alsa-gobject/pull/44 Patch URL : https://github.com/alsa-project/alsa-gobject/pull/44.patch Repository URL: https://github.com/alsa-project/alsa-gobject