userspace: Make network interface a kernel object

Make net_if a kernel object with type K_OBJ_NET_IF so that we
can restrict access to it.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
diff --git a/scripts/gen_kobject_list.py b/scripts/gen_kobject_list.py
index 5f12b80..b932581 100755
--- a/scripts/gen_kobject_list.py
+++ b/scripts/gen_kobject_list.py
@@ -103,6 +103,7 @@
     ("z_thread_stack_element", (None, False, False)),
     ("device", (None, False, False)),
     ("NET_SOCKET", (None, False, False)),
+    ("net_if", (None, False, False)),
     ("sys_mutex", (None, True, False)),
     ("k_futex", (None, True, False))
 ])