igb: force all queues to interrupt once every 2 seconds

Set the EICS bit for each of the RX queues at least once every 2 seconds to
prevent the rx queues from stalling.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>