Merge "Add missing <functional> header for std::function" into main am: 138e470f

Original change: https://android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/2673540



Change-Id: Idfce3bfac194b53cb5a74cbbffe869d8530231b1
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>