Update default MTU value to 1500 am: 0fd91c20 am: 0a3d47a5 am: 794bf5e4

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



Change-Id: I77dbcbccfca7b0c70517ba434c23f44997851000
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>