libstagefright: mpeg2ts: Ignore continuity_counter discontinuity

The continuity counter is incremented for each ts packet. Any lost
packet results in a discontinuity, and the stock parser flushes the
current frame data leading to corruption if an I-frame is lost.
Avoid flushing on discontinuity to prevent some of this corruption.

CRs-Fixed: 663391

Change-Id: I683269dcb36a1424f6d9a6e543cf9e1ead0103a7