core/sockets: Add missing socket services and functions from switchbrew

- Add Unknown39 and Unknown40 functions to BSD service for [20.0.0+]
- Implement bsd:nu service with ISfUserService and ISfAssignedNetworkInterfaceService
- Add dns:priv and ethc:c/ethc:i service stubs
- Update CMakeLists.txt to include new socket service files
- All new functions include basic stub implementations following existing patterns

This completes the socket services implementation based on switchbrew.org documentation.

Signed-off-by: Zephyron <zephyron@citron-emu.org>

src/core/hle/service/sockets/bsdnu.cpp

@@ -0,0 +1,87 @@
+// SPDX-FileCopyrightText: Copyright 2025 citron Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "core/hle/service/sockets/bsdnu.h"
+#include "core/hle/service/ipc_helpers.h"
+#include "core/hle/service/sockets/sockets.h"
+
+namespace Service::Sockets {
+
+ISfAssignedNetworkInterfaceService::ISfAssignedNetworkInterfaceService(Core::System& system_)
+    : ServiceFramework{system_, "ISfAssignedNetworkInterfaceService"} {
+    // clang-format off
+    static const FunctionInfo functions[] = {
+        {0, &ISfAssignedNetworkInterfaceService::AddSession, "AddSession"},
+    };
+    // clang-format on
+
+    RegisterHandlers(functions);
+}
+
+ISfAssignedNetworkInterfaceService::~ISfAssignedNetworkInterfaceService() = default;
+
+void ISfAssignedNetworkInterfaceService::AddSession(HLERequestContext& ctx) {
+    LOG_WARNING(Service, "(STUBBED) called AddSession");
+    IPC::ResponseBuilder rb{ctx, 2};
+    rb.Push(ResultSuccess);
+}
+
+ISfUserService::ISfUserService(Core::System& system_) : ServiceFramework{system_, "ISfUserService"} {
+    // clang-format off
+    static const FunctionInfo functions[] = {
+        {0, &ISfUserService::Assign, "Assign"},
+        {128, &ISfUserService::GetUserInfo, "GetUserInfo"},
+        {129, &ISfUserService::GetStateChangedEvent, "GetStateChangedEvent"},
+    };
+    // clang-format on
+
+    RegisterHandlers(functions);
+}
+
+ISfUserService::~ISfUserService() = default;
+
+void ISfUserService::Assign(HLERequestContext& ctx) {
+    LOG_WARNING(Service, "(STUBBED) called Assign");
+
+    IPC::ResponseBuilder rb{ctx, 2, 0, 1};
+    rb.Push(ResultSuccess);
+    rb.PushIpcInterface<ISfAssignedNetworkInterfaceService>(system);
+}
+
+void ISfUserService::GetUserInfo(HLERequestContext& ctx) {
+    LOG_WARNING(Service, "(STUBBED) called GetUserInfo");
+    IPC::ResponseBuilder rb{ctx, 4};
+    rb.Push(ResultSuccess);
+    rb.Push<s32>(-1);
+    rb.PushEnum(Errno::SUCCESS);
+}
+
+void ISfUserService::GetStateChangedEvent(HLERequestContext& ctx) {
+    LOG_WARNING(Service, "(STUBBED) called GetStateChangedEvent");
+    IPC::ResponseBuilder rb{ctx, 4};
+    rb.Push(ResultSuccess);
+    rb.Push<s32>(-1);
+    rb.PushEnum(Errno::SUCCESS);
+}
+
+BSDNU::BSDNU(Core::System& system_) : ServiceFramework{system_, "bsd:nu"} {
+    // clang-format off
+    static const FunctionInfo functions[] = {
+        {0, &BSDNU::CreateUserService, "CreateUserService"},
+    };
+    // clang-format on
+
+    RegisterHandlers(functions);
+}
+
+BSDNU::~BSDNU() = default;
+
+void BSDNU::CreateUserService(HLERequestContext& ctx) {
+    LOG_WARNING(Service, "(STUBBED) called CreateUserService");
+
+    IPC::ResponseBuilder rb{ctx, 2, 0, 1};
+    rb.Push(ResultSuccess);
+    rb.PushIpcInterface<ISfUserService>(system);
+}
+
+} // namespace Service::Sockets