calibrator: support compilation with a custom include dir and libnl3

These can be controlled via the NLROOT and NLVER environment variables.
See the Makefile for details.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
calibrator: write to correct filename during plt_tx_bip

This functions passes the filename to the calib_valid_handler callback.
If the filename is a local variable, this sometimes leads to reads from
corrupted memory, resulting in the wrong filename, or a crash.

Signed-off-by: Arik Nemtsov <arik@wizery.com>