Properly constrain use of nonces with AEAD crypto

[idra at samba.org]

The current AEAD crypto primitives we have access to and use (AES-128-CCM and
AES-128-GCM) have a very annoying failure mode if a nonce is ever reused with
the same key.
The attached patch adds checks to avoid ever wrapping and resusing a nonce.

It passes a custom autobuild.

Please review and push.
Simo.

-- 
Simo Sorce       idra at samba.org
-------------------------------
Samba Team http://www.samba.org
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