The current LOG_BUF size is a bit confusing the first
time that "make oldconfig" is used.  It's difficult to
select anything other than the default value.

Also, you (Linus) expressed a desire to have this
configurable only if DEBUG_KERNEL or "kernel hacking"
was enabled, so I've changed it to accomplish that.

This patch also uses Kconfig in a way that Roman intended
since a patch in 2.5.52 which enables default values if
a prompt is not enabled, but lets values be chosen when
the prompt is enabled.  You also asked for this in setting
this config option.