Kernel: Implement is_zero for RoutingDecision

Author: https://github.com/deoxxa
Commit: b15a7c435f
Pull-request: https://github.com/SerenityOS/serenity/pull/499
Reviewed-by: https://github.com/awesomekling

Kernel/Net/Routing.h

@@ -6,6 +6,8 @@ struct RoutingDecision
 {
     WeakPtr<NetworkAdapter> adapter;
     MACAddress next_hop;
+
+    bool is_zero() const;
 };
 
 RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source);