i40e: Leave debug_mask cleared at init

Don't set our internal debug_mask at startup unless we get specific signal
to from the debug module parameter.

This should take care of the issue with all the device capabilities getting
printed even when we hadn't asked for the debug info.

Change-ID: I7fbc6bd8b11ed9b0631ec018ff36015a04100b6c
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>