ifconfig debug enable

I doubt that network driver modules are compiled to do debugging by default; it would seriously slow down a system.
Looking at the ixgbe driver source, it looks like any "debug" printing statements do nothing.

To turn it on, you would have to change the driver source and build a custom kernel.
ixgbe have many INIT_DEBUGOUT, IOCTL_DEBUGOUT etc.
They are all translated to printf on condition DEBUG_INIT=0 etc.
But DEBUG_INIT does not consider ifconfig debug.
It seems need rebuild driver? :(