message: Fix OpenSSL 3 warning for curve selection
  It turns out that the new API was only introduced with OpenSSL 1.1.1 -
  so this sadly gets another ifdef.
diff: @@ -231,7 +231,17 @@ SSL_CTX* session::create_ssl_context() {
  #if defined(CAF_SSL_HAS_ECDH_AUTO) && (OPENSSL_VERSION_NUMBER < 0x10100000L)
  SSL_CTX_set_ecdh_auto(ctx, 1);
  #else
  +#if OPENSSL_VERSION_NUMBER < 0x10101000L
  + auto ecdh = EC_KEY_new_by_curve_name(NID_secp384r1);
  + if (!ecdh)
  + CAF_RAISE_ERROR("cannot get ECDH curve");
  + CAF_PUSH_WARNINGS
  + SSL_CTX_set_tmp_ecdh(ctx, ecdh);
  + EC_KEY_free(ecdh);
  + CAF_POP_WARNINGS
  +#else /* OPENSSL_VERSION_NUMBER < 0x10101000L */
  SSL_CTX_set1_groups_list(ctx, "P-384");
  +#endif /* OPENSSL_VERSION_NUMBER < 0x10101000L */
  #endif
  #ifdef CAF_SSL_HAS_SECURITY_LEVEL
  const char* cipher = "AECDH-AES256-SHA@SECLEVEL=0";
  