net: buf: Let's make use of func/line parameters when available

It clutters a bit the code with ifdefs but it's quite useful when
debugging.

Change-Id: I4f6899d052921b8ef8a7ec2f6e7df927a1bca2f1
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>