netlink: decode NETLINK_CRYPTO crypto_user_alg netlink attributes

netlink: decode NETLINK_CRYPTO crypto_user_alg netlink attributes

* configure.ac (AC_CHECK_TYPES): Check for crypto_report_aead,
crypto_report_blkcipher, crypto_report_cipher, crypto_report_hash,
and crypto_report_rng structures in <linux/cryptouser.h>.
* netlink_crypto.c (decode_crypto_report_generic,
decode_crypto_report_hash, decode_crypto_report_blkcipher,
decode_crypto_report_aead, decode_crypto_report_rng,
decode_crypto_report_cipher): New functions.
(crypto_user_alg_nla_decoders): New array.
(decode_crypto_user_alg): Use it.
* xlat/crypto_nl_attrs.in: New file.
* NEWS: Mention this.