unbound: Add AF_NETLINK to allowed address families.

Unbound throws the following error:

--8<---------------cut here---------------start------------->8---
error: failed to list interfaces: getifaddrs: Address family not supported by protocol
fatal error: could not open ports
--8<---------------cut here---------------end--------------->8---

The solution is pulled from upstream:
NLnetLabs/unbound#351

nixos/modules/services/networking/unbound.nix

@@ -195,7 +195,7 @@ in
         RuntimeDirectory = "unbound";
         ConfigurationDirectory = "unbound";
         StateDirectory = "unbound";
-        RestrictAddressFamilies = [ "AF_INET" "AF_INET6" "AF_UNIX" ];
+        RestrictAddressFamilies = [ "AF_INET" "AF_INET6" "AF_NETLINK" "AF_UNIX" ];
         RestrictRealtime = true;
         SystemCallArchitectures = "native";
         SystemCallFilter = [