Don't coalesce more than 250ms worth of encoded data into a single codec input buffer.

This currently only applies to the component OMX.TI.AAC.decode, it is the only one to support coalescing in the first place.

In certain edge cases (encoded audio track contains silence), each buffer would turn out to be an amazing 6(!!!) bytes, we'd spend lots and lots of time streaming network data to fill the codec's buffers of size 6144 bytes with .. silence.

Change-Id: I9f449f310fc64ca384bd02e4a783e33cf5b46fcc
related-to-bug: 2609049
QA-Impact: streamed (http) playback of aac audio content on Droid.