Set MTU to 1200 for CST because we reserve 80 bytes for VCN. am: a0f79d2964

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/services/Iwlan/+/20060527

Change-Id: Ic461e6cb55e0843fdb438cf6be92a1f2e0d93add
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>