Hearing Aid: use correct Data Length and MediaType

Adjusted the requested data length to the BT Controller from 168 to 167.
Also, change the default media type during playback to unknown.

Bug: 116317072
Bug: 116631303
Test: Manual testing with Hearing Aids and verifying with OTA logs
Change-Id: Ic4e934729a98bef5c10ebca64093d8a192e79a01
(cherry picked from commit d1c2f786)