bnx2: Use one handler for all MSI-X vectors.

Use the same MSI-X handler to schedule NAPI.  Change the dev_instance
void pointer to the bnx2_napi struct instead so we can have the proper
context for each MSI-X vector.

Add a new bnx2_poll_msix() that is optimized for handling MSI-X
NAPI polling of rx/tx work only.  Remove the old bnx2_tx_poll() that
is no longer needed.  Each MSI-X vector handles 1 tx and 1 rx ring.
The first vector handles link events as well.

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