libstagefright: Adjustment for TunnelPlayer buffer size

- Make necessary adjustments to align the buffer size
  for TunnelPlayer to satisfy the following conditions
- Buffer size is a multiple of LCM(1,2,4,6,8)
- Buffer size is aligned to 4k.
CRs-Fixed: 447274, 442365

Change-Id: I1b7f9ac3cf8ff86f972a8b6798bfcff3a4ba7c64