bnx2x: Protect against VFs' ndos when SR-IOV is disabled

Since SR-IOV can be activated dynamically and iproute2 can be called
asynchronously, the various callbacks need a robust sanity check before
attempting to access the SR-IOV database and members since there are numerous
states in which it can find the driver (e.g., PF is down, sriov was not enabled
yet, VF is down, etc.).

In many of the states the callback result will be null pointer dereference.

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>