VSI is set as default forwarding one when promisc mode is set for
PF interface, when PF is switched to switchdev mode or when VF
driver asks to enable allmulticast or promisc mode for the VF
interface (when vf-true-promisc-support priv flag is off).
The third case is buggy because in that case VSI associated with
VF remains as default one after VF removal.

Reproducer:
1. Create VF
   echo 1 > sys/class/net/ens7f0/device/sriov_numvfs
2. Enable allmulticast or promisc mode on VF
   ip link set ens7f0v0 allmulticast on
   ip link set ens7f0v0 promisc on
3. Delete VF
   echo 0 > sys/class/net/ens7f0/device/sriov_numvfs
4. Try to enable promisc mode on PF
   ip link set ens7f0 promisc on

Although it looks that promisc mode on PF is enabled the opposite
is true because ice_vsi_sync_fltr() responsible for IFF_PROMISC
handling first checks if any other VSI is set as default forwarding
one and if so the function does not do anything. At this point
it is not possible to enable promisc mode on PF without re-probe
device.

To resolve the issue this patch clear default forwarding VSI
during ice_vsi_release() when the VSI to be released is the default
one.

Fixes: 01b5e89a ("ice: Add VF promiscuous support")
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Alice Michael <alice.michael@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>