crypto: unify key_type creation code

crypto: unify key_type creation code

At the moment we have tls_crypt_kt() and auth_token_kt that basically do
the same thing, but with different algorithms used to initialise the
structure.

In order to avoid code duplication and copy/paste errors, unify code and
make it parametric, so that it can be re-used in various places.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20220217163159.7936-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg23831.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>