igb: fix memory leak when setting ring size while interface is down

Changing ring sizes while the interface was down was causing a double
allocation of the receive and transmit rings.  This issue is amplified when
there are multiple rings enabled.  To prevent this we need to add an
additional check which will just update the ring counts when the interface
is not up and skip the allocation steps.

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>