When using T2 virtual functions, it is important to properly stop DPDK and free the device.
Otherwise the virtual functions may be blocked and a restart of the admin application is necessary.

Up to now, SIGINT was shutting down the PHY simulators without freeing the device.
This commit adds a signal handler to handle SIGINT in a way that allow to properly free the device.
This feature is first added to the PHY simulators that use the T2 which are `nr_ulsim`, `nr_dlsim`, `nr_ulschsim` and `nr_dlschsim`.