[usecase-webapi][XWALK-1473] Fix bug for WebRTC

- Fix interface name
- Failure analysis: The ondatachannel event cannot be fired

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Tizen IVI]
Unit test result summary: pass 0, fail 1, block 0
Merge pull request #626 from yunxliu/yunxliu/misc/webrtc_modify

[usecase-webapi][XWALK-1473] Fix bug for WebRTC