tipc: Simplify log buffer resizing

This patch simplifies & standardizes the way TIPC's print buffer
log is resized.  Code to terminate use of the log buffer is
eliminated by simply setting the log buffer size to 0 bytes.

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