ice: Fix probe/open race condition

As soon as the driver registers the PF netdev, userspace utilities
like NetworkManager try to bring up the associated interface. When
this happens, the driver may not have finished initializing fully,
resulting in a bunch of errors in the interface up flow.

The driver already has a mechanism to indicate if it's not up yet;
by setting the __ICE_DOWN bit in pf->state, but this bit gets
cleared too early in the current flow. So clear this bit only when
the driver is fully up. Also check for the same bit in the ice_open
flow, and return -EBUSY if the bit is set.

Also in ice_open, replace references of vsi->back with a local
variable.

Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>