net: buf: Add extra logic when debug is enabled

In case of invalid behavior such as error or warnings print caller
function name and line number so it is easier to track back when there
there is a problem.

Change-Id: I3a5f4c7f63e0560fe0cf6f25936b079f127776a8
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>