NetworkTracePoller: fix a warning by explicitly capturing 'this' am: b055f15845

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/3248523

Change-Id: I757b4e38f48366a8f65214bcfe632010a2dc4f63
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>