tipc: reverse call order for link_reset()->node_link_down()

In many cases the call order when a link is reset goes as follows:
tipc_node_xx()->tipc_link_reset()->tipc_node_link_down()

This is not the right order if we want the node to be in control,
so in this commit we change the order to:
tipc_node_xx()->tipc_node_link_down()->tipc_link_reset()

The fact that tipc_link_reset() now is called from only one
location with a well-defined state will also facilitate later
simplifications of tipc_link_reset() and the link FSM.

Tested-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>