Implement the IpMemoryStore APIs that retrieve or store the network event count. am: 05b6c41063 am: 1599392ba8

Original change: https://android-review.googlesource.com/c/platform/packages/modules/NetworkStack/+/3244201

Change-Id: I8d7997f264e4ed6e449dc6feb9e59d25721ffc3c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>