nixos/systemd.network: add support for UseDomains= in [Network] sections

Those options were also added with systemd 256, but sadly were missed out in #307068.

These options are documented in:
- [systemd 256 changelog](https://github.com/systemd/systemd/releases/tag/v256) (search for `UseDomains=`)
- [networkd.conf(5)](https://www.freedesktop.org/software/systemd/man/256/networkd.conf.html#UseDomains=)
- [systemd.network(5)](https://www.freedesktop.org/software/systemd/man/256/systemd.network.html#UseDomains=)

nixos/modules/system/boot/networkd.nix

@@ -20,6 +20,7 @@ let
           "IPv6PrivacyExtensions"
           "IPv4Forwarding"
           "IPv6Forwarding"
+          "UseDomains"
         ])
         (assertValueOneOf "SpeedMeter" boolValues)
         (assertInt "SpeedMeterIntervalSec")
@@ -28,6 +29,7 @@ let
         (assertValueOneOf "IPv6PrivacyExtensions" (boolValues ++ ["prefer-public" "kernel"]))
         (assertValueOneOf "IPv4Forwarding" boolValues)
         (assertValueOneOf "IPv6Forwarding" boolValues)
+        (assertValueOneOf "UseDomains" (boolValues ++ ["route"]))
       ];
 
       sectionDHCPv4 = checkUnitConfig "DHCPv4" [
@@ -652,6 +654,7 @@ let
           "Address"
           "Gateway"
           "DNS"
+          "UseDomains"
           "Domains"
           "DNSDefaultRoute"
           "NTP"
@@ -705,6 +708,7 @@ let
         (assertValueOneOf "DNSSEC" (boolValues ++ ["allow-downgrade"]))
         (assertValueOneOf "LLDP" (boolValues ++ ["routers-only"]))
         (assertValueOneOf "EmitLLDP" (boolValues ++ ["nearest-bridge" "non-tpmr-bridge" "customer-bridge"]))
+        (assertValueOneOf "UseDomains" (boolValues ++ ["route"]))
         (assertValueOneOf "DNSDefaultRoute" boolValues)
         (assertRemoved "IPForward" "IPv4Forwarding and IPv6Forwarding in systemd.network(5) and networkd.conf(5)")
         (assertValueOneOf "IPv4Forwarding" boolValues)