gpg: Simplify the AEAD decryption function.
* g10/decrypt-data.c (aead_set_nonce, aead_set_ad): Merge into ... (aead_set_nonce_and_ad): new single function. Change callers. (decrypt_data): Do not set the nonce and ad here. (aead_underflow): Get rid of the LAST_CHUNK_DONE hack.
The main change here is that we now re-init the context only right
before we decrypt and not after a checktag.
- Signed-off-by: Werner Koch <wk@gnupg.org>