ExtMediaPlayer: Increase parcel pool size to 30

Increase MAX_NUM_PARCELS to 30. This is to handle
parcel override issue when textsamples are sent at
a fast pace from mediaplayer.
Usecase: With CEA CC streams, dashplayer sendTextPacket
embedded in each video sample as soon as decoded.
No realtime offset delay sync logic for text samples
as with A/V samples. When samples drained in batch,
can have more than 5 textsamples sent in flurry

Change-Id: I4c4c63b9c9c296dbb387c4da9e70c040b75f92b6