Correct registerNativeAllocation type

We're changing the argument type to long, since it should be roughly
large enough to hold a size_t everywhere.

We need to fall back to the old API when the new version might not yet
be available because we're running on an old platform version.

Test: Treehugger, boot AOSP
Change-Id: I057b25af8a46360373fb8c5cfad2be1fa3f3bdc0