ixgbe: fix memory leak when resizing rings while interface is down

This patch resolves a memory leak that occurs when you resize the rings via
the ethtool -G option while the interface is down.

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>