bna: Remove tx tasklet

The scheduling of tasklet and keeping the interrupts enabled makes interrupt
reduntant. 20% of the Tx interrupts have nothing left to process or could not
process as Tx tasklet was running.

Signed-off-by: Jing Huang <huangj@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>