tipc: Add missing locks when inspecting node list & link list

This patch ensures that TIPC configuration commands that display info
about neighboring nodes and their links take the spinlocks that
protect the node list and link lists from changing while the lists
are being traversed.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>