NetworkTracePoller: fix a warning by explicitly capturing 'this' am: b055f15845 am: ed6511eb5f

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

Change-Id: I5c4abd395f7c396794759103e4e84544917a2aad
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>