lib: Exec func on each netns

Added possibility to run some func on each netns.

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
diff --git a/include/namespace.h b/include/namespace.h
index 52f7fbd..a2ac7dc 100644
--- a/include/namespace.h
+++ b/include/namespace.h
@@ -44,5 +44,11 @@
 
 extern int netns_switch(char *netns);
 extern int netns_get_fd(const char *netns);
+extern int netns_foreach(int (*func)(char *nsname, void *arg), void *arg);
+
+struct netns_func {
+	int (*func)(char *nsname, void *arg);
+	void *arg;
+};
 
 #endif /* __NAMESPACE_H__ */