gpg: Print info about the used AEAD algorithm in the compliance msg.

* g10/misc.c (openpgp_cipher_algo_mode_name): New.
* g10/decrypt-data.c (decrypt_data): Use function here.
--

Note that openpgp_cipher_algo_mode_name is different from the version
2.2 becuase we append ".CFB" here.

Without this change we would see

  gpg: cipher algorithm 'AES256' may not be used in
  --compliance=de-vs mode

This is confusing because AES256 is compliant.  Now we see

  gpg: cipher algorithm 'AES256.OCB' may not be used in
  --compliance=de-vs mode

which gives a hint on the problem.

1 files changed, 2 insertions, 0 deletions

diff --git a/g10/main.h b/g10/main.h
index e5308744a..0525732f2 100644
--- a/g10/main.h
+++ b/g10/main.h
@@ -126,6 +126,8 @@ enum gcry_cipher_algos map_cipher_openpgp_to_gcry (cipher_algo_t algo);
 int openpgp_cipher_blocklen (cipher_algo_t algo);
 int openpgp_cipher_test_algo(cipher_algo_t algo);
 const char *openpgp_cipher_algo_name (cipher_algo_t algo);
+const char *openpgp_cipher_algo_mode_name (cipher_algo_t algo,
+                                           aead_algo_t aead);
 
 gpg_error_t openpgp_aead_test_algo (aead_algo_t algo);
 const char *openpgp_aead_algo_name (aead_algo_t algo);