tipc: Elimination of print buffer chaining

This patch revamps TIPC's print buffer subsystem to eliminate
support for arbitrary chains of print buffers, which were
rarely needed and difficult to use safely.

In its place, print buffers can now be configured to echo their
output to the system console.  This provides an equivalent for
the only chaining currently utilized by TIPC, in a faster and
more compact manner.

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