ANDROID: fips140: use full 16-byte IV

By using the initial_value parameter when creating the pycryptodome
AES-CTR instance, we can use any 16-byte IV, like the other AES modes.
Therefore, there's no need for the last 4 bytes of the IV to be 0.
This doesn't really matter, but it seems nice to avoid this quirk.

Bug: 153614920
Bug: 188620248
Change-Id: If33de260b1119f2b3e004164199b08364781ab23
Signed-off-by: Eric Biggers <ebiggers@google.com>