Abstract EVP cipher context creation

The EVP_CIPHER_CTX is now created inside a wrapper function to add support
for OpenSSL 1.1. Also fixed improper use of the EVP_CIPHER_CTX internals
in binlogrouter.

include/maxscale/encryption.h

@@ -0,0 +1,25 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cdefs.h>
+
+#include <openssl/evp.h>
+
+MXS_BEGIN_DECLS
+
+
+EVP_CIPHER_CTX* mxs_evp_cipher_ctx_alloc();
+void mxs_evp_cipher_ctx_free(EVP_CIPHER_CTX* ctx);
+
+MXS_END_DECLS