Expand coverage of different buffer sizes.

Expand coverage of different buffer sizes.

- When -z is used, include small buffers from 1 to 32 bytes to test
  stream ciphers.  Note that while AES-XTS claims to support a block
  size of 1 in OpenSSL, it does require a minimum of 1 block of cipher
  text as it is not a stream cipher but depends on CTS to pad out the
  final partial block.

- Permit multiple AAD sizes to be set via multiple -A options, or via
  -z.  When -z is set, use small buffers from 0 to 32 bytes followed
  by powers of 2 up to 256.  When multiple sizes are specified, the
  ETA and AEAD algorithms perform the full matrix of AAD sizes by
  payload sizes.

- Only warn on unchanged ciphertext instead of erroring.  The
  currently generated plaintext and key for a couple of AES-CTR tests
  with a buffer size of 1 results in ciphertext that matches the
  plaintext.

Reviewed by:	cem
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D25006