tipc: Add missing spinlock in name table display code

This patch ensures that the display code that traverses the
publication lists belonging to a name table entry take its
associated spinlock, to protect against a possible change to
one of its "head of list" pointers caused by a simultaneous
name table lookup operation by another thread of control.

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