io/i2c: document the test case fields; test against a 10-bit addr
io/i2c: document the test case fields; test against a 10-bit addr

Change-Id: Id4dabd60fdadf22fcde414d107d3c07e0dbcb842
Reviewed-on: https://go-review.googlesource.com/22620
Reviewed-by: Johan Euphrosine <aeff70c2aef2cec1cd2754756b5d3e6402001c31@google.com>
Reviewed-by: Jaana Burcu Dogan <347c19a639ce752a783b4ea325d6539ab4b4a262@google.com>

golang/exp,golang/exp,golang/exp