[CRYPTO] Allow CTR mode on smaller size blocks
[CRYPTO] Allow CTR mode on smaller size blocks

Previously CTR-mode required buffers that are a multiple of 16 (AES
block size); since CTR can work as a stream cipher, the test was
updated to allow for encryption/decryption of any sized block with
CTR.

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core