Start of work on passing around StrictMode policy over Binder calls.

This is (intendend to be) a no-op change.

At this stage, Binder RPCs just have an additional uint32 passed around
in the header, right before the interface name.  But nothing is actually
done with them yet.  That value should right now always be 0.

This now boots and seems to work.

Change-Id: I135b7c84f07575e6b9717fef2424d301a450df7b