macsec: Support VLAN-filtering lower devices

macsec: Support VLAN-filtering lower devices

VLAN-filtering is done through two netdev features
(NETIF_F_HW_VLAN_CTAG_FILTER and NETIF_F_HW_VLAN_STAG_FILTER) and two
netdev ops (ndo_vlan_rx_add_vid and ndo_vlan_rx_kill_vid).

Implement these and advertise the features if the lower device supports
them. This allows proper VLAN filtering to work on top of MACsec
devices, when the lower device is capable of VLAN filtering.
As a concrete example, having this chain of interfaces now works:
vlan_filtering_capable_dev(1) -> macsec_dev(2) -> macsec_vlan_dev(3)

Before the mentioned commit this used to accidentally work because the
MACsec device (and thus the lower device) was put in promiscuous mode
and the VLAN filter was not used. But after commit [1] correctly made
the macsec driver expose the IFF_UNICAST_FLT flag, promiscuous mode was
no longer used and VLAN filters on dev 1 kicked in. Without support in
dev 2 for propagating VLAN filters down, the register_vlan_dev ->
vlan_vid_add -> __vlan_vid_add -> vlan_add_rx_filter_info call from dev
3 is silently eaten (because vlan_hw_filter_capable returns false and
vlan_add_rx_filter_info silently succeeds).

For MACsec, VLAN filters are only relevant for offload, otherwise
the VLANs are encrypted and the lower devices don't care about them. So
VLAN filters are only passed on to lower devices in offload mode.
Flipping between offload modes now needs to offload/unoffload the
filters with vlan_{get,drop}_rx_*_filter_info().

To avoid the back-and-forth filter updating during rollback, the setting
of macsec->offload is moved after the add/del secy ops. This is safe
since none of the code called from those requires macsec->offload.

In case adding the filters fails, the added ones are rolled back and an
error is returned to the operation toggling the offload state.

Fixes: 0349659fd72f ("macsec: set IFF_UNICAST_FLT priv flag")
Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20260408115240.1636047-5-cratiu@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>