gve: implement DQO TX datapath for AF_XDP zero-copy

In the descriptor clean path, a number of changes need to be made to
accommodate out of order completions and double completions.

The XSK stack can only handle completions being processed in order, as a
single counter is incremented in xsk_tx_completed to sigify how many XSK
descriptors have been completed. Because completions can come back out
of order in DQ, a separate queue of XSK descriptors must be maintained.
This queue keeps the pending packets in the order that they were written
so that the descriptors can be counted in xsk_tx_completed in the same
order.

For double completions, a new pending packet state and type are
introduced. The new type, GVE_TX_PENDING_PACKET_DQO_XSK, plays an
anlogous role to pre-existing _SKB and _XDP_FRAME pending packet types
for XSK descriptors. The new state, GVE_PACKET_STATE_XSK_COMPLETE,
represents packets for which no more completions are expected. This
includes packets which have received a packet completion or reinjection
completion, as well as packets whose reinjection completion timer have
timed out. At this point, such packets can be counted as part of
xsk_tx_completed() and freed.

Reviewed-by: Willem de Bruijn <[email protected]>
Signed-off-by: Praveen Kaligineedi <[email protected]>
Signed-off-by: Joshua Washington <[email protected]>
Signed-off-by: Jeroen de Borst <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

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