S2io: Fixed synchronization between scheduling of napi with card reset and close

- Fixed synchronization between scheduling of napi with card reset and close
  by moving the enabling and disabling of napi to card up and card down
  functions respectively instead of open and close.

Signed-off-by: Surjit Reang <surjit.reang@neterion.com>
Signed-off-by: Ramkrishna Vepa <ram.vepa@neterion.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>