src/config/network.rs: always write bridge_ports and bond_slaves

So that we can reliable detect the interface type.

src/config/network.rs

@@ -142,31 +142,31 @@ impl Interface {
     /// Write attributes not dependening on address family
     fn write_iface_attributes(&self, w: &mut dyn Write) -> Result<(), Error> {
 
+        static EMPTY_LIST: Vec<String> = Vec::new();
+
         match self.interface_type {
             NetworkInterfaceType::Bridge => {
                 if let Some(true) = self.bridge_vlan_aware {
                     writeln!(w, "\tbridge-vlan-aware yes")?;
                 }
-                if let Some(ref ports) = self.bridge_ports {
+                let ports = self.bridge_ports.as_ref().unwrap_or(&EMPTY_LIST);
                 if ports.is_empty() {
                     writeln!(w, "\tbridge-ports none")?;
                 } else {
                     writeln!(w, "\tbridge-ports {}", ports.join(" "))?;
                 }
             }
-            }
             NetworkInterfaceType::Bond => {
                 let mode = self.bond_mode.unwrap_or(LinuxBondMode::balance_rr);
                 writeln!(w, "\tbond-mode {}", bond_mode_to_str(mode))?;
 
-                if let Some(ref slaves) = self.slaves {
+                let slaves = self.slaves.as_ref().unwrap_or(&EMPTY_LIST);
                 if slaves.is_empty() {
                     writeln!(w, "\tbond-slaves none")?;
                 } else {
                     writeln!(w, "\tbond-slaves {}", slaves.join(" "))?;
                 }
             }
-            }
             _ => {}
         }