The "Miscellaneous Node" fell through cracks of node initialisation,
as its ID is shared with HN-I.
This patch treats MN as a special case (which it is), adding separate
validation check for it and pre-defining the node ID in relevant events
descriptions. That way one can simply run:
# perf stat -a -e ccn/mn_ecbarrier/ <workload>
Additionally, direction in the MN pseudo-events XP watchpoint
definitions is corrected to be "TX" (1) as they are defined from the
crosspoint point of view (thus barriers are transmitted from XP to MN).