dhcp: use nm_dhcp_option_create_options_dict() in nm_dhcp_client_handle_event()

The point of using this trivial helper function is to have one function
that is related to the construction of the options dictionary, that we
can search for.

It answers the question, where do we create a option hash (at `git grep
nm_dhcp_option_create_options_dict`).

src/core/dhcp/nm-dhcp-client.c

@@ -1613,7 +1613,7 @@ nm_dhcp_client_handle_event(gpointer               unused,
         GVariant                      *value;
 
         /* Copy options */
-        str_options = g_hash_table_new_full(nm_str_hash, g_str_equal, g_free, g_free);
+        str_options = nm_dhcp_option_create_options_dict(FALSE);
         g_variant_iter_init(&iter, options);
         while (g_variant_iter_next(&iter, "{&sv}", &name, &value)) {
             maybe_add_option(self, str_options, name, value);