mbedtls: fix segfault by calling mbedtls_cipher_free() in cipher_ctx_free()

mbedtls: fix segfault by calling mbedtls_cipher_free() in cipher_ctx_free()

Commit ("openssl: Fix compilation without deprecated OpenSSL 1.1 APIs")
has removed the cipher_ctx_cleanup() API, as it is not anymore required
to be a distinct call. However, while doing so it also touched the
mbedtls backend in a wrong way causing a systematic segfault upon
connection.

Basically mbedtls_cipher_free(ctx) was moved from the defunct
cipher_ctx_cleanup()
to md_ctx_free(), while it was supposed to go into cipher_ctx_free().
This was clearly wrong as also the type of the ctx variable was not
correct anymore.

Fix this mistake by actually moving mbedtls_cipher_free(ctx) to
cipher_ctx_free().

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20190816204945.7937-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg18781.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>