tipc: add net set to new netlink api

Add TIPC_NL_NET_SET command to the new tipc netlink API.

This command can set the network id and network (tipc) address.

Netlink logical layout of network set message:
-> net
     [ -> id ]
     [ -> address ]

Signed-off-by: Richard Alpe <richard.alpe@ericsson.com>
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>