Unfortunately, C++ does not support designated initializers.  Add a function
that helps fill their place.

Use example:

-static struct netisr_handler ether_nh = {
-       .nh_name = "ether",
-       .nh_handler = ether_nh_input,
-       .nh_proto = NETISR_ETHER,
-       .nh_policy = NETISR_POLICY_SOURCE,
-       .nh_dispatch = NETISR_DISPATCH_DIRECT,
-};
+static netisr_handler ether_nh = initialize_with([] (netisr_handler& x) {
+       x.nh_name = "ether";
+       x.nh_handler = ether_nh_input;
+       x.nh_proto = NETISR_ETHER;
+       x.nh_policy = NETISR_POLICY_SOURCE;
+       x.nh_dispatch = NETISR_DISPATCH_DIRECT;
+});

Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>