Make Fuchsia signal matching nonexhaustive

Change-Id: Ifdc3b46575afdfe45b951da2eef7c3147bda22d3
diff --git a/src/sys/fuchsia/selector.rs b/src/sys/fuchsia/selector.rs
index 52ca7d7..1c669a4 100644
--- a/src/sys/fuchsia/selector.rs
+++ b/src/sys/fuchsia/selector.rs
@@ -174,6 +174,10 @@
                 // User packets are only ever sent by an Awakener
                 return Ok(true);
             }
+            _ => {
+                info!("Unrecognized packet");
+                return Ok(true);
+            }
         };
 
         let key = packet.key();