Get node_from, node_to ids from state instead of props when a new link appears.

This is more reliable than assuming the link carries the id of its nodes, as there have been cases where a link was created without those
properties set.
Instead, we can just pull them from the state via the port ids of the link.

src/main.rs

@@ -37,7 +37,11 @@ enum PipewireMessage {
         direction: Direction,
     },
     /// A new link has appeared.
-    LinkAdded { id: u32, link: PipewireLink },
+    LinkAdded {
+        id: u32,
+        port_from: u32,
+        port_to: u32,
+    },
     /// An object was removed
     ObjectRemoved { id: u32 },
 }