Change line/channel names from tapi/1 and tapi/2 to tapi/0 and tapi1

Unsupported lines/channes like TAPI/[2-6], BRCM/6 are also removed.

This change has the following benefits.
- To simplify the line/channel name handling in /etc/init.d/voice_client
- To have the consistent implementation both on Intel and on Broadcom platforms

(cherry picked from commit 40c426ca)