Hi,
since DPDK 21.11 is out, we should start discussion to make asymmetric API stable.

-              Struct rte_crypto_vec vs struct rte_crypto_param_t

We have two almost identical functionally structs, one in _sym.h another in asym.h so we probably should pick one of them.
"rte_crypto_vec" additionally contains total length which will be useful information as PMD will overwrite "len" in many cases.
Unfortunately as "rte_crypto.h" includes "_sym.h" and "_asym.h" not other way around we cannot move it to "rte_crypto.h" but asymmetric will include symmetric anyway so it probably will not be that big of an issue.

-              Network byte order

               rte_crypto_param dP; /**<
               /**< dP - Private CRT component
               * Private CRT component of RSA parameter  required for CRT method
               * RSA private key operations in Octet-string network byte order
               * format.
               * dP = d mod ( p - 1 )
               */
We have plenty of these (sometimes in places where should not be, and not in places where should). Every member that contains this comment here is a big integer in big-endian format.
We could simplify it to:

/** Big integer in big-endian format */
typedef struct rte_crypto_vec rte_crypto_bigint;

               rte_crypto_bigint dP; /**< d mod ( p - 1 ) */

ED related algorithms like (EDDSA) will use little-endian bit integers so it will have to use different approach.