bnx2x: Prevent VF race

bnx2x: Prevent VF race

The mail box containing the Vf-Pf messages is susceptible
to a race - it's possible for 2 flows to try and write commands,
causing one to override the other's message.
Use a mutex to synchronize the access, preventing said race.

Signed-off-by: Dmitry Kravkov <[email protected]>
Signed-off-by: Yuval Mintz <[email protected]>
Signed-off-by: Ariel Elior <[email protected]>
Signed-off-by: David S. Miller <[email protected]>