Read NAT keepalive value from carrier config am: f0eb7b81 am: 4c60d9a4 am: 2137519e

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/2452265



Change-Id: Ifd24f7072d3781b2050f5c63956a17b86db0394b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>