Expose self.sockets in Interface via iterators

This is needed to not loose access to methods on sockets, e.g. iterating
over them and closing or checking which ports are being used.

src/iface/interface.rs

@@ -555,6 +555,16 @@ where
         &mut self.device
     }
 
+    /// Get an iterator to the inner sockets.
+    pub fn sockets(&self) -> impl Iterator<Item = &Socket<'a>> {
+        self.sockets.iter()
+    }
+
+    /// Get a mutable iterator to the inner sockets.
+    pub fn sockets_mut(&mut self) -> impl Iterator<Item = &mut Socket<'a>> {
+        self.sockets.iter_mut()
+    }
+
     /// Add an address to a list of subscribed multicast IP addresses.
     ///
     /// Returns `Ok(announce_sent)` if the address was added successfully, where `annouce_sent`