Add a default ON flag for DNS fail-fast feature

This is an emergency stop button if any unexpected regression is
reported.

Bug: 309739930
Test: atest resolv_integration_test
(cherry picked from https://android-review.googlesource.com/q/commit:08422a0dcb5e93da7f7be65e5e5237c64b1000f7)
Merged-In: Ib6aa5f619e34e3da33b82586d3e78b4fed5a666b
Change-Id: Ib6aa5f619e34e3da33b82586d3e78b4fed5a666b