net/mlx4_core: Don't disable SRIOV if there are active VFs

When unloading the host driver while there are VFs active on VMs,
the PF driver disabled sriov anyway, causing kernel crashes.

We now leave SRIOV enabled, to avoid that.

When the driver is reloaded, __mlx4_init_one is invoked on the PF.
It now checks to see if SRIOV is already enabled on the PF -- and
if so does not enable sriov again.

Signed-off-by: Tal Alon <talal@mellanox.com>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>