Update default MTU value to 1500 am: 0fd91c20 am: 6288cf76 am: 57c0bd76 am: 8b563424

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/opt/telephony/+/18819055



Change-Id: Ie828eb0fc0a952934277118d3903cfa3c164944c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>