Kernel/Net: Get the correct interface type in SIOCGIFHWADDR ioctl

When calling ioctl on a socket with SIOCGIFHWADDR, return the correct
physical interface type. This value was previously hardcoded to
ARPHRD_ETHER (Ethernet), and now can also return ARPHRD_LOOPBACK for the
loopback adapter.

Kernel/Net/IPv4Socket.cpp

@@ -740,7 +740,16 @@ ErrorOr<void> IPv4Socket::ioctl(OpenFileDescription&, unsigned request, Userspac
 
         case SIOCGIFHWADDR: {
             auto mac_address = adapter->mac_address();
-            ifr.ifr_hwaddr.sa_family = ARPHRD_ETHER; // FIXME: Query the underlying network interface for it's type
+            switch (adapter->adapter_type()) {
+            case NetworkAdapter::Type::Loopback:
+                ifr.ifr_hwaddr.sa_family = ARPHRD_LOOPBACK;
+                break;
+            case NetworkAdapter::Type::Ethernet:
+                ifr.ifr_hwaddr.sa_family = ARPHRD_ETHER;
+                break;
+            default:
+                VERIFY_NOT_REACHED();
+            }
             mac_address.copy_to(Bytes { ifr.ifr_hwaddr.sa_data, sizeof(ifr.ifr_hwaddr.sa_data) });
             return copy_to_user(user_ifr, &ifr);
         }

Kernel/Net/Intel/E1000NetworkAdapter.h

@@ -33,6 +33,7 @@ public:
 
     virtual StringView purpose() const override { return class_name(); }
     virtual StringView device_name() const override { return "E1000"sv; }
+    virtual Type adapter_type() const override { return Type::Ethernet; }
 
 protected:
     static constexpr size_t rx_buffer_size = 8192;

Kernel/Net/LoopbackAdapter.h

@@ -22,6 +22,7 @@ public:
 
     virtual void send_raw(ReadonlyBytes) override;
     virtual StringView class_name() const override { return "LoopbackAdapter"sv; }
+    virtual Type adapter_type() const override { return Type::Loopback; }
     virtual bool link_up() override { return true; }
     virtual bool link_full_duplex() override { return true; }
     virtual int link_speed() override { return 1000; }

Kernel/Net/NetworkAdapter.h

@@ -47,11 +47,17 @@ class NetworkAdapter
     : public AtomicRefCounted<NetworkAdapter>
     , public LockWeakable<NetworkAdapter> {
 public:
+    enum class Type {
+        Loopback,
+        Ethernet
+    };
+
     static constexpr i32 LINKSPEED_INVALID = -1;
 
     virtual ~NetworkAdapter();
 
     virtual StringView class_name() const = 0;
+    virtual Type adapter_type() const = 0;
     virtual ErrorOr<void> initialize(Badge<NetworkingManagement>) = 0;
 
     StringView name() const { return m_name->view(); }

Kernel/Net/Realtek/RTL8168NetworkAdapter.h

@@ -35,6 +35,7 @@ public:
 
     virtual StringView purpose() const override { return class_name(); }
     virtual StringView device_name() const override { return class_name(); }
+    virtual Type adapter_type() const override { return Type::Ethernet; }
 
 private:
     // FIXME: should this be increased? (maximum allowed here is 1024) - memory usage vs packet loss chance tradeoff