Revert DNS cache flush command deletion from "Cleanup: Delete dead code."

This reverts part of commit 7a161c535104555890fa78b99faf1f414fc03e85.
The DNS cache flushing code needs to be called when routes change.

Change-Id: I20d39eabfa088deeeeeff0c3292b1910fd948b0d
bug:16549455
2 files changed