xfrm: fix the return code when xfrm_*_register_afinfo failed

If xfrm_*_register_afinfo failed since xfrm_*_afinfo[afinfo->family] had the
value, return the -EEXIST, not -ENOBUFS
Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_input.c

@@ -29,7 +29,7 @@ int xfrm_input_register_afinfo(struct xfrm_input_afinfo *afinfo)
 		return -EAFNOSUPPORT;
 	spin_lock_bh(&xfrm_input_afinfo_lock);
 	if (unlikely(xfrm_input_afinfo[afinfo->family] != NULL))
-		err = -ENOBUFS;
+		err = -EEXIST;
 	else
 		rcu_assign_pointer(xfrm_input_afinfo[afinfo->family], afinfo);
 	spin_unlock_bh(&xfrm_input_afinfo_lock);

net/xfrm/xfrm_policy.c

@@ -2808,7 +2808,7 @@ int xfrm_policy_register_afinfo(struct xfrm_policy_afinfo *afinfo)
 		return -EAFNOSUPPORT;
 	spin_lock(&xfrm_policy_afinfo_lock);
 	if (unlikely(xfrm_policy_afinfo[afinfo->family] != NULL))
-		err = -ENOBUFS;
+		err = -EEXIST;
 	else {
 		struct dst_ops *dst_ops = afinfo->dst_ops;
 		if (likely(dst_ops->kmem_cachep == NULL))

net/xfrm/xfrm_state.c

@@ -1908,7 +1908,7 @@ int xfrm_state_register_afinfo(struct xfrm_state_afinfo *afinfo)
 		return -EAFNOSUPPORT;
 	spin_lock_bh(&xfrm_state_afinfo_lock);
 	if (unlikely(xfrm_state_afinfo[afinfo->family] != NULL))
-		err = -ENOBUFS;
+		err = -EEXIST;
 	else
 		rcu_assign_pointer(xfrm_state_afinfo[afinfo->family], afinfo);
 	spin_unlock_bh(&xfrm_state_afinfo_lock);