net: mvpp2: fix XDP rx queues registering

The registration of XDP queue information is incorrect because the
RX queue id we use is invalid. When port->id == 0 it appears to works
as expected yet it's no longer the case when port->id != 0.

The problem arised while using a recent kernel version on the
MACCHIATOBin. This board has several ports:
 * eth0 and eth1 are 10Gbps interfaces ; both ports has port->id == 0;
 * eth2 is a 1Gbps interface with port->id != 0.

Code from xdp-tutorial (more specifically advanced03-AF_XDP) was used
to test packet capture and injection on all these interfaces. The XDP
kernel was simplified to:

	SEC("xdp_sock")
	int xdp_sock_prog(struct xdp_md *ctx)
	{
		int index = ctx->rx_queue_index;

		/* A set entry here means that the correspnding queue_id
		* has an active AF_XDP socket bound to it. */
		if (bpf_map_lookup_elem(&xsks_map, &index))
			return bpf_redirect_map(&xsks_map, index, 0);

		return XDP_PASS;
	}

Starting the program using:

	./af_xdp_user -d DEV

Gives the following result:

 * eth0 : ok
 * eth1 : ok
 * eth2 : no capture, no injection

Investigating the issue shows that XDP rx queues for eth2 are wrong:
XDP expects their id to be in the range [0..3] but we found them to be
in the range [32..35].

Trying to force rx queue ids using:

	./af_xdp_user -d eth2 -Q 32

fails as expected (we shall not have more than 4 queues).

When we register the XDP rx queue information (using
xdp_rxq_info_reg() in function mvpp2_rxq_init()) we tell it to use
rxq->id as the queue id. This value is computed as:

	rxq->id = port->id * max_rxq_count + queue_id

where max_rxq_count depends on the device version. In the MACCHIATOBin
case, this value is 32, meaning that rx queues on eth2 are numbered
from 32 to 35 - there are four of them.

Clearly, this is not the per-port queue id that XDP is expecting:
it wants a value in the range [0..3]. It shall directly use queue_id
which is stored in rxq->logic_rxq -- so let's use that value instead.

rxq->id is left untouched ; its value is indeed valid but it should
not be used in this context.

This is consistent with the remaining part of the code in
mvpp2_rxq_init().

With this change, packet capture is working as expected on all the
MACCHIATOBin ports.

Fixes: b27db227

 ("mvpp2: use page_pool allocator")
Signed-off-by: Louis Amas <louis.amas@eho.link>
Signed-off-by: Emmanuel Deloget <emmanuel.deloget@eho.link>
Reviewed-by: Marcin Wojtas <mw@semihalf.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Link: https://lore.kernel.org/r/20211207143423.916334-1-louis.amas@eho.link
Signed-off-by: Jakub Kicinski <kuba@kernel.org>