ice: virtchnl: stop pretending to support RSS over AQ or registers

[ Upstream commit 2652b99e ]

The E800 series hardware uses the same iAVF driver as older devices,
including the virtchnl negotiation scheme.

This negotiation scheme includes a mechanism to determine what type of RSS
should be supported, including RSS over PF virtchnl messages, RSS over
firmware AdminQ messages, and RSS via direct register access.

The PF driver will always prefer VIRTCHNL_VF_OFFLOAD_RSS_PF if its
supported by the VF driver. However, if an older VF driver is loaded, it
may request only VIRTCHNL_VF_OFFLOAD_RSS_REG or VIRTCHNL_VF_OFFLOAD_RSS_AQ.

The ice driver happily agrees to support these methods. Unfortunately, the
underlying hardware does not support these mechanisms. The E800 series VFs
don't have the appropriate registers for RSS_REG. The mailbox queue used by
VFs for VF to PF communication blocks messages which do not have the
VF-to-PF opcode.

Stop lying to the VF that it could support RSS over AdminQ or registers, as
these interfaces do not work when the hardware is operating on an E800
series device.

In practice this is unlikely to be hit by any normal user. The iAVF driver
has supported RSS over PF virtchnl commands since 2016, and always defaults
to using RSS_PF if possible.

In principle, nothing actually stops the existing VF from attempting to
access the registers or send an AQ command. However a properly coded VF
will check the capability flags and will report a more useful error if it
detects a case where the driver does not support the RSS offloads that it
does.

Fixes: 1071a835 ("ice: Implement virtchnl commands for AVF support")
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Alan Brady <alan.brady@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>