extract_x509_extension(): hide status message during normal operation.

For each recognized extension in a certificate, extract_x509_extension()
would issue an "ASN1 ERROR: can not handle field type" debug message at
verb 2. Reduce that to verb 9 (D_TLS_ERRORS -> D_TLS_DEBUG) and alter the
message text accordingly.

Signed-off-by: Andris Kalnozols <andris@hpl.hp.com>
Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <53E6A61C.7010106@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8981
Signed-off-by: Gert Doering <gert@greenie.muc.de>