ldn: Implement calls of UserLocalCommunicationService (#829)

* ldn: Implement calls of UserLocalCommunicationService

- Implement `IUserServiceCreator: CreateUserLocalCommunicationService` according to RE.
- Implement `IUserLocalCommunicationService` calls:
  - Every calls in this interface are layered to `NetworkInterface`.
  - `GetState` according to RE.
  - `InitializeOld`, `Initialize` and `Finalize` stubbed with the appropriate result code and some TODO according to RE.
  - `AttachStateChangeEvent` according to RE.

* Fix var name and TODO comments

* Fix review

Ryujinx.HLE/HOS/Services/Ldn/UserServiceCreator/IUserLocalCommunicationService.cs

@@ -0,0 +1,88 @@
+using Ryujinx.HLE.HOS.Ipc;
+using Ryujinx.HLE.HOS.Kernel.Common;
+using Ryujinx.HLE.HOS.Services.Ldn.Types;
+using System;
+using System.Net;
+
+namespace Ryujinx.HLE.HOS.Services.Ldn.UserServiceCreator
+{
+    class IUserLocalCommunicationService : IpcService
+    {
+        // TODO(Ac_K): Determine what the hardcoded unknown value is.
+        private const int UnknownValue = 90;
+
+        private NetworkInterface _networkInterface;
+
+        private int _stateChangeEventHandle = 0;
+
+        public IUserLocalCommunicationService(ServiceCtx context)
+        {
+            _networkInterface = new NetworkInterface(context.Device.System);
+        }
+
+        [Command(0)]
+        // GetState() -> s32 state
+        public ResultCode GetState(ServiceCtx context)
+        {
+            if (_networkInterface.NifmState != ResultCode.Success)
+            {
+                context.ResponseData.Write((int)NetworkState.Error);
+
+                return ResultCode.Success;
+            }
+
+            ResultCode result = _networkInterface.GetState(out NetworkState state);
+
+            if (result == ResultCode.Success)
+            {
+                context.ResponseData.Write((int)state);
+            }
+
+            return result;
+        }
+
+        [Command(100)]
+        // AttachStateChangeEvent() -> handle<copy>
+        public ResultCode AttachStateChangeEvent(ServiceCtx context)
+        {
+            if (_stateChangeEventHandle == 0)
+            {
+                if (context.Process.HandleTable.GenerateHandle(_networkInterface.StateChangeEvent.ReadableEvent, out _stateChangeEventHandle) != KernelResult.Success)
+                {
+                    throw new InvalidOperationException("Out of handles!");
+                }
+            }
+
+            context.Response.HandleDesc = IpcHandleDesc.MakeCopy(_stateChangeEventHandle);
+
+            // Return ResultCode.InvalidArgument if handle is null, doesn't occur in our case since we already throw an Exception.
+
+            return ResultCode.Success;
+        }
+
+        [Command(400)]
+        // InitializeOld(u64, pid)
+        public ResultCode InitializeOld(ServiceCtx context)
+        {
+            return _networkInterface.Initialize(UnknownValue, 0, null, null);
+        }
+
+        [Command(401)]
+        // Finalize()
+        public ResultCode Finalize(ServiceCtx context)
+        {
+            return _networkInterface.Finalize();
+        }
+
+        [Command(402)] // 7.0.0+
+        // Initialize(u64 ip_addresses, u64, pid)
+        public ResultCode Initialize(ServiceCtx context)
+        {
+            // TODO(Ac_K): Determine what addresses are.
+            IPAddress unknownAddress1 = new IPAddress(context.RequestData.ReadUInt32());
+            IPAddress unknownAddress2 = new IPAddress(context.RequestData.ReadUInt32());
+
+            return _networkInterface.Initialize(UnknownValue, version: 1, unknownAddress1, unknownAddress2);
+        }
+    }
+}