net/sched: act_ct: Always fill offloading tuple iifidx

Referenced commit doesn't always set iifidx when offloading the flow to
hardware. Fix the following cases:

- nf_conn_act_ct_ext_fill() is called before extension is created with
nf_conn_act_ct_ext_add() in tcf_ct_act(). This can cause rule offload with
unspecified iifidx when connection is offloaded after only single
original-direction packet has been processed by tc data path. Always fill
the new nf_conn_act_ct_ext instance after creating it in
nf_conn_act_ct_ext_add().

- Offloading of unidirectional UDP NEW connections is now supported, but ct
flow iifidx field is not updated when connection is promoted to
bidirectional which can result reply-direction iifidx to be zero when
refreshing the connection. Fill in the extension and update flow iifidx
before calling flow_offload_refresh().

Fixes: 9795ded7f924 ("net/sched: act_ct: Fill offloading tuple iifidx")
Reviewed-by: Paul Blakey <paulb@nvidia.com>
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Fixes: 6a9bad0069cf ("net/sched: act_ct: offload UDP NEW connections")
Link: https://lore.kernel.org/r/20231103151410.764271-1-vladbu@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched: act_ct: Fill offloading tuple iifidx

Driver offloading ct tuples can use the information of which devices
received the packets that created the offloaded connections, to
more efficiently offload them only to the relevant device.

Add new act_ct nf conntrack extension, which is used to store the skb
devices before offloading the connection, and then fill in the tuple
iifindex so drivers can get the device via metadata dissector match.

Signed-off-by: Oz Shlomo <ozsh@nvidia.com>
Signed-off-by: Paul Blakey <paulb@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>