Renamed W5500 -> Device, added an Interface struct that should implement the embedded-nal traits, used it to internalize the mutability of the device

src/interface.rs

@@ -0,0 +1,21 @@
+use bus::{ActiveBus};
+use device::Device;
+use network::Network;
+use core::cell::RefCell;
+
+pub struct Interface<SpiBus: ActiveBus, NetworkImpl: Network> {
+    pub device: RefCell<Device<SpiBus, NetworkImpl>>,
+}
+
+impl<SpiBus: ActiveBus, NetworkImpl: Network> Interface<SpiBus, NetworkImpl> {
+    fn new(device: Device<SpiBus, NetworkImpl>) -> Self {
+        Self { device: RefCell::new(device) }
+    }
+}
+
+impl<SpiBus: ActiveBus, NetworkImpl: Network> From<Device<SpiBus, NetworkImpl>> for Interface<SpiBus, NetworkImpl> {
+    fn from(device: Device<SpiBus, NetworkImpl>) -> Interface<SpiBus, NetworkImpl> {
+        Interface::<SpiBus, NetworkImpl>::new(device)
+    }
+}
+