NetworkProvider: add missing synchronization am: aecfab5f72

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2148673

Change-Id: I9e222c3fb8d78811795f52a9f5b42fa5be422855
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>