momentarily go back to 16 byte IVs

The Crypto provider used from Android P onwards (conscrypt) has a weird bug
that when 12 bytes IVs are used it will decrypt or encrypt the entire file
in RAM instead of streaming it. That will cause OOM for 'larger' files on http
upload. (both downloads and uploads are effected)

It is currently unclear why this is happening and why Conscrypt is put into a
different mode.
We are only observing that Android versions below P are fine and using 16 bytes
is fine on all Android versions.