xfrm: Move device notifications to a sepatate file

This is needed for the upcomming IPsec device offloading.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 159342f..ac984da 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1443,6 +1443,7 @@
 void xfrm_init(void);
 void xfrm4_init(void);
 int xfrm_state_init(struct net *net);
+void xfrm_dev_init(void);
 void xfrm_state_fini(struct net *net);
 void xfrm4_state_init(void);
 void xfrm4_protocol_init(void);