sctp: protocol.c call rcu_barrier() on unload.

On module unload call rcu_barrier(), this is needed as synchronize_rcu()
is not strong enough.  The kmem_cache_destroy() does invoke
synchronize_rcu() but it does not provide same protection.
Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/protocol.c

@@ -1370,6 +1370,8 @@ SCTP_STATIC __exit void sctp_exit(void)
 	sctp_proc_exit();
 	cleanup_sctp_mibs();
 
+	rcu_barrier(); /* Wait for completion of call_rcu()'s */
+
 	kmem_cache_destroy(sctp_chunk_cachep);
 	kmem_cache_destroy(sctp_bucket_cachep);
 }