added missing flavor-rxtx extention to api-ref page

bug: #1097363

Patchset adds explanation of rxtx to first line displayed
(rather than hiding it under details button).

Change-Id: I9ce3e99ad63176d63ff428eb120b997bfec7b60f
author: diane fleming
Merge "added missing flavor-rxtx extention to api-ref page"