dns: effectively disable host ttl (#1786)
dns: effectively disable host ttl (#1786)

Description: On mobile, backgrounding might cause the host to be past its TTL without good reason. Given the host would be deleted, and new streams for a given domain would have to wait for resolution, it is better to not delete existing hosts; especially since deletion only happens when re-resolving is already in progress. There is no way to disable so the value below is equivalent to 24 hours.
Risk Level: low
Testing: CI

Signed-off-by: Jose Nino <ca94e32c82b10963d0ce6eadf427a615ff7d1c0b@lyft.com>
envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile