Add the option allow the users to set a different buffer size for the
trace. For example, in large systems, the user might be interested on
reducing the trace buffer to avoid large tracing files.

The buffer size is specified in kB, and it is only affecting
the tracing instance.

The function trace_set_buffer_size() appears on libtracefs v1.6,
so increase the minimum required version on Makefile.config.

Link: https://lkml.kernel.org/r/e7c9ca5b3865f28e131a49ec3b984fadf2d056c6.1715860611.git.bristot@kernel.org

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>