Revert "l3cfg: do not add dependent routes for non-default routes"

We must trust l3cfg when generating dependent onlink routes for all kind
of routes not default routes only. This was done by
"nm_platform_ip_route_sync()" so there is not change in behaviour at
all.

"nm_platform_ip_route_sync()" could be needed for other situation where
l3cfg cannot add the dependent onlink routes, so we are not removing
that logic.

This reverts commit 6b4123db1c.

(cherry picked from commit 9c492c6fc4)

src/core/nm-l3-config-data.c

@@ -2569,8 +2569,7 @@ nm_l3_config_data_add_dependent_onlink_routes(NML3ConfigData *self, int addr_fam
         if (nm_ip_addr_is_null(addr_family, p_gateway))
             continue;
 
-        if (!NM_PLATFORM_IP_ROUTE_IS_DEFAULT(route_src)
-            || _data_get_direct_route_for_host(
+        if (_data_get_direct_route_for_host(
                 self,
                 addr_family,
                 p_gateway,