Kernel: Take a copy of MACAddress in RoutingDecision

Author: https://github.com/deoxxa
Commit: 302d521485
Pull-request: https://github.com/SerenityOS/serenity/pull/499
Reviewed-by: https://github.com/awesomekling

Kernel/Net/Routing.h

@@ -5,7 +5,7 @@
 struct RoutingDecision
 {
     WeakPtr<NetworkAdapter> adapter;
-    const MACAddress& next_hop;
+    MACAddress next_hop;
 };
 
 RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source);