xfrm: fix xfrm_dev_event() missing when compile without CONFIG_XFRM_OFFLOAD

In commit d77e38e6 ("xfrm: Add an IPsec hardware offloading API") we
make xfrm_device.o only compiled when enable option CONFIG_XFRM_OFFLOAD.
But this will make xfrm_dev_event() missing if we only enable default XFRM
options.

Then if we set down and unregister an interface with IPsec on it. there
will no xfrm_garbage_collect(), which will cause dev usage count hold and
get error like:

unregister_netdevice: waiting for <dev> to become free. Usage count = 4

Fixes: d77e38e6 ("xfrm: Add an IPsec hardware offloading API")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

include/net/xfrm.h

@@ -1850,8 +1850,9 @@ static inline struct xfrm_offload *xfrm_offload(struct sk_buff *skb)
 }
 #endif
 
-#ifdef CONFIG_XFRM_OFFLOAD
 void __net_init xfrm_dev_init(void);
+
+#ifdef CONFIG_XFRM_OFFLOAD
 int validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t features);
 int xfrm_dev_state_add(struct net *net, struct xfrm_state *x,
 		       struct xfrm_user_offload *xuo);
@@ -1877,10 +1878,6 @@ static inline void xfrm_dev_state_free(struct xfrm_state *x)
 	}
 }
 #else
-static inline void __net_init xfrm_dev_init(void)
-{
-}
-
 static inline int validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t features)
 {
 	return 0;

net/xfrm/Makefile

@@ -4,8 +4,7 @@
 
 obj-$(CONFIG_XFRM) := xfrm_policy.o xfrm_state.o xfrm_hash.o \
 		      xfrm_input.o xfrm_output.o \
-		      xfrm_sysctl.o xfrm_replay.o
-obj-$(CONFIG_XFRM_OFFLOAD) += xfrm_device.o
+		      xfrm_sysctl.o xfrm_replay.o xfrm_device.o
 obj-$(CONFIG_XFRM_STATISTICS) += xfrm_proc.o
 obj-$(CONFIG_XFRM_ALGO) += xfrm_algo.o
 obj-$(CONFIG_XFRM_USER) += xfrm_user.o

net/xfrm/xfrm_device.c

@@ -22,6 +22,7 @@
 #include <net/xfrm.h>
 #include <linux/notifier.h>
 
+#ifdef CONFIG_XFRM_OFFLOAD
 int validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t features)
 {
 	int err;
@@ -137,6 +138,7 @@ bool xfrm_dev_offload_ok(struct sk_buff *skb, struct xfrm_state *x)
 	return true;
 }
 EXPORT_SYMBOL_GPL(xfrm_dev_offload_ok);
+#endif
 
 int xfrm_dev_register(struct net_device *dev)
 {