httplive: fix issues during httplive streaming seek

- Cache the new seek position during the last seek progress.
- Before starting the fetchers, check whether one new seek
  operation comes. If yes, reset to change the configuration
  based on the last cached seek position.
- This change can avoid ignoring the new seek operation before
  finishing the last seek progress.

Change-Id: I2a99198881d023b7afc0ec310395e2f86d7105d9
Crs-Fixed: 623264