Refactor SocketNetlinkMonitor to make it buildable with system sdk am: 6e12ac60b8

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2524596

Change-Id: Ia2a8c3a14549af1364c234889f7c63ac367afc5d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>