bnx2x: Fix VF stats sync

Since the PF gathers statistics for the VF, when the VF is about to unload
we must synchronize the release of its statistics buffer with the PF, so that
no DMA operation will be made to that address after the buffer release.

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