Read NAT keepalive value from carrier config am: f0eb7b81 am: 4c60d9a4 am: 2137519e am: 4abc14b5

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



Change-Id: If8da10980110b7babf434265e6bc836fd2815433
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>