Set/get broadcast address in TunInterface

Modelled after TunInterface's IPV4 logic.
Uses SIOCGIFBRDADDR & SIOCSIFBRDADDR.
View https://man7.org/linux/man-pages/man7/netdevice.7.html.

tun/tests/configure.rs

@@ -9,6 +9,21 @@ fn test_create() {
     TunInterface::new()?;
 }
 
+#[test]
+#[throws]
+#[cfg(not(any(target_os = "windows", target_vendor = "apple")))]
+fn test_set_get_broadcast_addr() {
+    let tun = TunInterface::new()?;
+    let addr = Ipv4Addr::new(10, 0, 0, 1);
+    tun.set_ipv4_addr(addr)?;
+
+    let broadcast_addr = Ipv4Addr::new(255, 255, 255, 0);
+    tun.set_broadcast_addr(broadcast_addr)?;
+    let result = tun.broadcast_addr()?;
+
+    assert_eq!(broadcast_addr, result);
+}
+
 #[test]
 #[throws]
 #[cfg(not(target_os = "windows"))]