bnx2x: handle known but unsupported VF messages

Commit b9871bcf "bnx2x: VF RSS support - PF side" has deprecated one of
the previous existing messages. If an old VF driver were to send this message
to the PF then the PF will not reply and leave the mailbox in an unsteady
state (and cause a timeout on the VF side).

Wait until firmware ack is written before unlocking channel

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>