[RFC] how to handle AAD copy operation for algif_aead

Hi Herbert et al,

attached are two patches where each patch has a different approach to copy the 
AAD in the algif_aead operation. I would like to hear your opinion which 
approach should be taken.

The patch 0001-crypto-algif_aead-copy-AAD-from-src-to-dst_separate.patch 
simply copies the AAD over from TX SGL to RX SGL. The pro is that the patch is 
small. The con is that this approach does *not* provide an in-place crypto 
operation.

The patch 0001-crypto-algif_aead-copy-AAD-from-src-to-dst_inplace.patch copies 
the AAD and the PT/CT from TX SGL into the RX SGL. In addition, this patch 
chains the SGL with the tag value part present in the TX SGL to the RX SGL in 
case of decryption. This implies that we have an in-place cipher operation 
operating in the RX SGL. Though, the patch is significantly larger.

(note: the patches are NOT meant for inclusion, but only for discussion -- yet 
both code parts are fully tested with by test framework in libkcapi).

Ciao
Stephan