made openssl_err_as_string static to avoid conflicts with other ciphers that would also use their own function - those can't rely on the AES module being there

transform_aes.c

@@ -77,7 +77,7 @@ static int transop_deinit_aes(n2n_trans_op_t *arg) {
 #ifdef OPENSSL_1_1
 /* get any erorr message out of openssl
    taken from https://en.wikibooks.org/wiki/OpenSSL/Error_handling */
-char *openssl_err_as_string (void) {
+static char *openssl_err_as_string (void) {
   BIO *bio = BIO_new (BIO_s_mem ());
   ERR_print_errors (bio);
   char *buf = NULL;