dnsmasq: Disable DNS server updation via STDIN on Brillo.

Brillo starts dnsmasq with STDIN redirected to /dev/null and we don't
need the feature to update the DNS servers via STDIN. So, disabling the
feature (commit id: 33b34445) for Brillo devices.

BUG: 25193399
TEST: Manual tests below:
1. Bootstrapped Edison and connected to a Wifi AP.
2. Verified the `top` output to ensure that dnsmasq wasn't hogging CPU.
3. Verified via `strace` that dnsmasq is no longer listening to /dev/null.

Change-Id: Ibc7c671a933904471b76ac6ce20f8490c9b0856c
3 files changed