bpf: simplify xdp_convert_ctx_access for xdp_rxq_info

As pointed out by Daniel Borkmann, using bpf_target_off() is not
necessary for xdp_rxq_info when extracting queue_index and
ifindex, as these members are u32 like BPF_W.

Also fix trivial spelling mistake introduced in same commit.

Fixes: 02dd329 ("bpf: finally expose xdp_rxq_info to XDP bpf-programs")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/uapi/linux/bpf.h

@@ -899,7 +899,7 @@ struct xdp_md {
 	__u32 data;
 	__u32 data_end;
 	__u32 data_meta;
-	/* Below access go though struct xdp_rxq_info */
+	/* Below access go through struct xdp_rxq_info */
 	__u32 ingress_ifindex; /* rxq->dev->ifindex */
 	__u32 rx_queue_index;  /* rxq->queue_index  */
 };

net/core/filter.c

@@ -4310,16 +4310,15 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
 				      si->dst_reg, si->dst_reg,
 				      offsetof(struct xdp_rxq_info, dev));
 		*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
-				      bpf_target_off(struct net_device,
-						     ifindex, 4, target_size));
+				      offsetof(struct net_device, ifindex));
 		break;
 	case offsetof(struct xdp_md, rx_queue_index):
 		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct xdp_buff, rxq),
 				      si->dst_reg, si->src_reg,
 				      offsetof(struct xdp_buff, rxq));
 		*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
-				      bpf_target_off(struct xdp_rxq_info,
-						queue_index, 4, target_size));
+				      offsetof(struct xdp_rxq_info,
+					       queue_index));
 		break;
 	}