Merge "Speculatively fix L2TP keepalive issues by reducing mtu" am: 392b52f49f am: 926d1ee880 am: 649c2bbbd8 am: 72432ab0f4

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1399646

Change-Id: Iba6098badc018fa64b1c5fc20177b97a81a2e685