There was a problem reported to us where the addition of a VF with an IPv6
address ending with a particular sequence would cause the parent device on
the PF to no longer be able to respond to neighbor discovery packets.

In this case, we had an ovs-bridge device living on top of a VLAN, which
was on top of a PF, and it would not be able to talk anymore (the neighbor
entry would expire and couldn't be restored).

The root cause of the issue is that if the PF is asked to be in IFF_PROMISC
mode (promiscuous mode) and it had an ipv6 address that needed the
33:33:ff:00:00:04 multicast address to work, then when the VF was added
with the need for the same multicast address, the VF would steal all the
traffic destined for that address.

The ice driver didn't auto-subscribe a request of IFF_PROMISC to the
"multicast replication from other port's traffic" meaning that it won't get
for instance, packets with an exact destination in the VF, as above.

The VF's IPv6 address, which adds a "perfect filter" for 33:33:ff:00:00:04,
results in no packets for that multicast address making it to the PF (which
is in promisc but NOT "multicast replication").

The fix is to enable "multicast promiscuous" whenever the driver is asked
to enable IFF_PROMISC, and make sure to disable it when appropriate.

Fixes: e94d4478 ("ice: Implement filter sync, NDO operations and bump version")
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>