can: af_can: export can_sock_destruct()

In j1939 we need our own struct sock::sk_destruct callback. Export the
generic af_can can_sock_destruct() that allows us to chain-call it.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Signed-off-by: Oleksij Rempel <[e-mail]>

include/linux/can/core.h

···
 			      void *data);
 
 extern int can_send(struct sk_buff *skb, int loop);
+void can_sock_destruct(struct sock *sk);
 
 #endif /* !_CAN_CORE_H */

net/can/af_can.c

···
 
 /* af_can socket functions */
 
-static void can_sock_destruct(struct sock *sk)
+void can_sock_destruct(struct sock *sk)
 {
 	skb_queue_purge(&sk->sk_receive_queue);
 	skb_queue_purge(&sk->sk_error_queue);
 }
+EXPORT_SYMBOL(can_sock_destruct);
 
 static const struct can_proto *can_get_proto(int protocol)
 {