Kernel+LibC: Stub out getifaddrs() and freeifaddrs()

These are required for some ports.

Userland/Libraries/LibC/ifaddrs.cpp

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibC/errno.h>
+#include <LibC/ifaddrs.h>
+
+int getifaddrs(struct ifaddrs**)
+{
+    errno = ENOSYS;
+    return -1;
+}
+
+void freeifaddrs(struct ifaddrs*)
+{
+}