Replace deprecated mbedtls DRBG update function

Replace deprecated mbedtls DRBG update function

The function mbedtls_ctr_drbg_update is deprecated as of mbedtls 2.16
and is superseded by mbedtls_ctr_drbg_update_ret, which returns an error
code. This commit replaces the call to the deprecated function with the
new one and logs a warning in case of an error.

For older versions of mbedtls, we add a compatibility function that runs
mbedtls_ctr_drbg_update and returns 0.

Signed-off-by: Max Fillinger <maximilian.fillinger@foxcrypto.com>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Message-Id: <20210810061644.20353-1-maximilian.fillinger@foxcrypto.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22711.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>