add Linux network namespace support for TUN device

Change-Id: Idd0ad8fa9c8e7ba0aeec1b52947598d4d297b620
diff --git a/lib/netns.h b/lib/netns.h
new file mode 100644
index 0000000..168e44f
--- /dev/null
+++ b/lib/netns.h
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2014-2017, Travelping GmbH <info@travelping.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef __NETNS_H
+#define __NETNS_H
+
+#if defined(__linux__)
+
+void init_netns(void);
+
+int switch_ns(int nsfd, sigset_t *oldmask);
+void restore_ns(sigset_t *oldmask);
+
+int open_ns(int nsfd, const char *pathname, int flags);
+int socket_ns(int nsfd, int domain, int type, int protocol);
+int get_nsfd(const char *name);
+
+#endif
+
+#endif