tree 1b3b637ae8f54205ad829dd83eb6c24dcad32416
parent caf8deb58af8a5480d325ab443d5c49649222456
author Zhihai Xu <zhihaixu@google.com> 1379300377 -0700
committer Zhihai Xu <zhihaixu@google.com> 1387227372 -0800

should return correct length and use shorter poll time for ad2p data

the default poll timeout(100ms) is too long for a2dp data read,
because the a2dp timer pertiod to read data is 20ms. The poll timeout
should be far less than a2dp timer pertiod. also when poll timeout happen
for read, we should return the data length which we already read instead of 0.

bug:8252054
Change-Id: Ifa8587c6b7d127cbbbff76d9e20b630303b6379f