tipc: fix message importance range check

Commit 3b4f302d85 ("tipc: eliminate
redundant locking") introduced a bug by removing the sanity check
for message importance, allowing programs to assign any value to
the msg_user field. This will mess up the packet reception logic
and may cause random link resets.

Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/port.h

@@ -179,8 +179,10 @@ static inline int tipc_port_importance(struct tipc_port *port)
 	return msg_importance(&port->phdr);
 }
 
-static inline void tipc_port_set_importance(struct tipc_port *port, int imp)
+static inline int tipc_port_set_importance(struct tipc_port *port, int imp)
 {
+	if (imp > TIPC_CRITICAL_IMPORTANCE)
+		return -EINVAL
 	msg_set_importance(&port->phdr, (u32)imp);
 }