bnx2x: Add missing bit in default Tx switching

Commit c14db202

 "bnx2x: Correct default Tx switching behaviour" supposedly
changed the default Tx switching behaviour, but was missing the fastpath change
required for FW to pass packets from PFs to VFs.

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>