S2io: code Optimization of isr function

- Code Optimization of s2io_isr function.
- Isr check using per device napi variable instead of driver global.
- Reduced from 3 to 1 if condition before check for processing packet receive
  packets.
- Implemented Jeff's comment to use synchronize_irq. Removed the isr_cnt
  variable as it became redundant.
- One time de assert the interrupts by writing all F's to the general_int_mask
  register instead of de asserting by clearing the source of interrupts with
  multiple writes which causes loss of interrupts (race conditions). It is
  entirely possible that before the driver has a chance to mask the asserted
  alarm bit, another alarm/traffic interrupt bit gets asserted as well. In
  this case Herc will keep the INTA line asserted and the bridge will not
  send a new Assert_INTA message upstream.

[ Resolved conflicts due to napi_struct changes... -DaveM ]

Signed-off-by: Sivakumar Subramani <sivakumar.subramani@neterion.com>
Signed-off-by: Santosh Rastapur <santosh.rastapur@neterion.com>
Signed-off-by: Ramkrishna Vepa <ram.vepa@neterion.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>