bna: TX Queue Depth Fix

sk_buff unmap_array grows greater than 65536 (x2) with Tx ring of 65536.
Reducing TXQ depth and safe(max) acking of Tx events to 32768 (same as Rx).
Add defines for TX and RX queue depths.

Signed-off-by: Gurunatha Karaje <gkaraje@brocade.com>
Signed-off-by: Rasesh Mody <rmody@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>