tipc: add node get/dump to new netlink api

tipc: add node get/dump to new netlink api

Add TIPC_NL_NODE_GET to the new tipc netlink API.

This command can dump the address and node status of all nodes in the
tipc cluster.

Netlink logical layout of returned node/address data:
-> node
    -> address
    -> up flag

Signed-off-by: Richard Alpe <[email protected]>
Reviewed-by: Erik Hugne <[email protected]>
Reviewed-by: Jon Maloy <[email protected]>
Acked-by: Ying Xue <[email protected]>
Signed-off-by: David S. Miller <[email protected]>