[BNX2]: Introduce new bnx2_napi structure.

Introduce a bnx2_napi structure that will hold a napi_struct and
other fields to handle NAPI polling for the napi_struct.  Various tx
and rx indexes and status block pointers will be moved from the main
bnx2 structure to this bnx2_napi structure.

Most NAPI path functions are modified to be passed this bnx2_napi
struct pointer.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>