Kernel: Use WeakPtr<NetworkAdapter> instead of NetworkAdapter* in net code

Author: https://github.com/deoxxa
Commit: 54ceabd48d
Pull-request: https://github.com/SerenityOS/serenity/pull/421
Reviewed-by: https://github.com/awesomekling ✅

Kernel/Net/Routing.cpp

@@ -1,10 +1,10 @@
 #include <Kernel/Net/LoopbackAdapter.h>
 #include <Kernel/Net/Routing.h>
 
-NetworkAdapter* adapter_for_route_to(const IPv4Address& ipv4_address)
+WeakPtr<NetworkAdapter> adapter_for_route_to(const IPv4Address& ipv4_address)
 {
     // FIXME: Have an actual routing table.
     if (ipv4_address == IPv4Address(127, 0, 0, 1))
-        return &LoopbackAdapter::the();
+        return LoopbackAdapter::the().make_weak_ptr();
     return NetworkAdapter::from_ipv4_address(IPv4Address(192, 168, 5, 2));
 }