ref(iroh-net): Don't write the match as fully exhaustive (#2585)

## Description

This makes it a bit earier to read.  It's harder to figure out if thre
are changes to the ConnectionType though, but let's assume that
doesn't happen too often.


## Breaking Changes

None

## Notes & open questions

I'm open to other ways of structuring this code.  Not entirely sure
what the best shape would be.

## Change checklist

- [x] Self-review.
- [x] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.
- [x] Tests if relevant.
- [x] All breaking changes documented.

iroh-net/src/magicsock/node_map/node_state.rs

@@ -303,46 +303,31 @@ impl NodeState {
 
             // Update some metrics
             match (prev_typ, typ) {
-                (ConnectionType::Direct(_), ConnectionType::Direct(_)) => (),
-                (ConnectionType::Direct(_), ConnectionType::Relay(_)) => {
-                    inc!(MagicsockMetrics, num_direct_conns_removed);
-                    inc!(MagicsockMetrics, num_relay_conns_added);
-                }
-                (ConnectionType::Direct(_), ConnectionType::Mixed(_, _)) => {
-                    inc!(MagicsockMetrics, num_direct_conns_removed);
-                    inc!(MagicsockMetrics, num_relay_conns_added);
-                }
-                (ConnectionType::Direct(_), ConnectionType::None) => {
-                    inc!(MagicsockMetrics, num_direct_conns_removed)
-                }
-                (ConnectionType::Relay(_), ConnectionType::Direct(_)) => {
-                    inc!(MagicsockMetrics, num_direct_conns_added);
-                    inc!(MagicsockMetrics, num_relay_conns_removed);
-                }
-                (ConnectionType::Relay(_), ConnectionType::Relay(_)) => (),
-                (ConnectionType::Relay(_), ConnectionType::Mixed(_, _)) => (),
-                (ConnectionType::Relay(_), ConnectionType::None) => {
-                    inc!(MagicsockMetrics, num_relay_conns_removed)
-                }
-                (ConnectionType::Mixed(_, _), ConnectionType::Direct(_)) => {
+                (ConnectionType::Relay(_), ConnectionType::Direct(_))
+                | (ConnectionType::Mixed(_, _), ConnectionType::Direct(_)) => {
                     inc!(MagicsockMetrics, num_direct_conns_added);
                     inc!(MagicsockMetrics, num_relay_conns_removed);
                 }
-                (ConnectionType::Mixed(_, _), ConnectionType::Relay(_)) => (),
-                (ConnectionType::Mixed(_, _), ConnectionType::Mixed(_, _)) => (),
-                (ConnectionType::Mixed(_, _), ConnectionType::None) => {
-                    inc!(MagicsockMetrics, num_relay_conns_removed)
+                (ConnectionType::Direct(_), ConnectionType::Relay(_))
+                | (ConnectionType::Direct(_), ConnectionType::Mixed(_, _)) => {
+                    inc!(MagicsockMetrics, num_direct_conns_removed);
+                    inc!(MagicsockMetrics, num_relay_conns_added);
                 }
                 (ConnectionType::None, ConnectionType::Direct(_)) => {
                     inc!(MagicsockMetrics, num_direct_conns_added)
                 }
-                (ConnectionType::None, ConnectionType::Relay(_)) => {
-                    inc!(MagicsockMetrics, num_relay_conns_added)
+                (ConnectionType::Direct(_), ConnectionType::None) => {
+                    inc!(MagicsockMetrics, num_direct_conns_removed)
                 }
-                (ConnectionType::None, ConnectionType::Mixed(_, _)) => {
+                (ConnectionType::None, ConnectionType::Relay(_))
+                | (ConnectionType::None, ConnectionType::Mixed(_, _)) => {
                     inc!(MagicsockMetrics, num_relay_conns_added)
                 }
-                (ConnectionType::None, ConnectionType::None) => (),
+                (ConnectionType::Relay(_), ConnectionType::None)
+                | (ConnectionType::Mixed(_, _), ConnectionType::None) => {
+                    inc!(MagicsockMetrics, num_relay_conns_removed)
+                }
+                _ => (),
             }
         }
         (best_addr, relay_url)