bna: TX Path and RX Path Changes

Change details:
 - Add bnad_pci_unmap_skb() API to unmap skb from transmit path and update the
   unmap index. Add more checks for illegal skbs in transmit path. Add tx_skb
   counters for dropped skbs.
 - The unmap_cons index used in bnad_free_txbufs() is incorrectly declared as
   u16. It quickly wraps around and accesses null sk_buff ptr. So using u32 to
   handle unmap_array.
 - Disable and enable interrupts from the same polling context to prevent
   reordering in Rx path.
 - Add Rx NAPI debug counters.
 - Make NAPI budget check more generic.
 - Modify dim timer stop logic to make it dependent on cfg and run flags
 - Handle reduced MSI-X vectors case in bnad_enable_msix.
 - Check for single frame TSO skbs and send them out as non-TSO.
 - Put memory barrier after bna_txq_prod_indx_doorbell().

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>