Remove reuse of key_type during init of data channel auth and tls-auth

Remove reuse of key_type during init of data channel auth and tls-auth

Prepare for using AEAD cipher modes + tls-auth, as tls-auth might want to
use an HMAC, while the data channel uses e.g. GCM tags.  This separates
the two initialisations.  Also, error out (and give a clear error message)
if a user specifies tls-auth but no valid auth algorithm, which makes no
sense at all.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1454874438-5081-3-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/11073
Signed-off-by: Gert Doering <gert@greenie.muc.de>