bnx2x: fix panic when TX ring is full

bnx2x: fix panic when TX ring is full

There is a off by one error in the minimal number of BD in
bnx2x_start_xmit() and bnx2x_tx_int() before stopping/resuming tx queue.

A full size GSO packet, with data included in skb->head really needs
(MAX_SKB_FRAGS + 4) BDs, because of bnx2x_tx_split()

This error triggers if BQL is disabled and heavy TCP transmit traffic
occurs.

bnx2x_tx_split() definitely can be called, remove a wrong comment.

Reported-by: Tomas Hruby <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Cc: Eilon Greenstein <[email protected]>
Cc: Yaniv Rosner <[email protected]>
Cc: Merav Sicron <[email protected]>
Cc: Tom Herbert <[email protected]>
Cc: Robert Evans <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Signed-off-by: David S. Miller <[email protected]>