Fix clang warnings related to OpenSSL 1.x

When CI tests are run locally on machine without OpenSSL 3.0, there are
some warnings during clang-tidy scan. They are related to unsupported
c-style code (implicit bool/int conversion, casting, and varagrs
functions). This change is fixing all of them, without changing
functionality.

Testing done:
- running docker image with UTs on local Ubuntu machine with SSL 1.1 is
  passing all tests, and no clang errors are reported.

Signed-off-by: Szymon Dompke <szymon.dompke@intel.com>
Change-Id: I5ec91db8f02f487786811afad77080137bab3c9a
diff --git a/include/ssl_key_handler.hpp b/include/ssl_key_handler.hpp
index 30145f8..1213758 100644
--- a/include/ssl_key_handler.hpp
+++ b/include/ssl_key_handler.hpp
@@ -350,12 +350,12 @@
         pKey = EVP_PKEY_new();
         if (pKey != nullptr)
         {
-            if (EVP_PKEY_assign_EC_KEY(pKey, myecc))
+            if (EVP_PKEY_assign(pKey, EVP_PKEY_EC, myecc) != 0)
             {
                 /* pKey owns myecc from now */
                 if (EC_KEY_check_key(myecc) <= 0)
                 {
-                    fprintf(stderr, "EC_check_key failed.\n");
+                    std::cerr << "EC_check_key failed.\n";
                 }
             }
         }