igb: set num_rx/tx_queues to 0 when queues are freed

An issue was seen on suspend in which the system reported a page fault.  This
was due to the new reg_idx code being called after the queues were freed.

This update prevents any for loops from going through the queues by setting
the number of queues to 0 when they are freed.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>