S2IO: Save/Restore unused buffer mappings in 2/3 buffer mode

- Save/Restore unused buffer mappings in 2/3 buffer mode to avoid
frequent mapping

- Save/Restore adapter reset count during adapter reset

  (Resending; forgot to cc netdev)

Signed-off-by: Santosh Rastapur <santosh.rastapur@neterion.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>