The AF_ALG socket family is the userspace interface for linux
crypto API, this patch adds af_alg family support and some common
functions for af_alg backend. It'll be used by afalg-backend crypto
latter.
Signed-off-by: NLongpeng(Mike) <longpeng2@huawei.com>

Maintainer: modified to report an error if AF_ALG is requested
but cannot be supported
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>