selftests/bpf: Convert bpf_iter_test_kern{3, 4}.c to define own bpf_iter_meta

b9f4c01f ("selftest/bpf: Make bpf_iter selftest compilable against old vmlinux.h")
missed the fact that bpf_iter_test_kern{3,4}.c are not just including
bpf_iter_test_kern_common.h and need similar bpf_iter_meta re-definition
explicitly.

Fixes: b9f4c01f ("selftest/bpf: Make bpf_iter selftest compilable against old vmlinux.h")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200519192341.134360-1-andriin@fb.com

tools/testing/selftests/bpf/progs/bpf_iter_test_kern3.c

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__task bpf_iter__task___not_used
 #include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__task
 #include <bpf/bpf_helpers.h>
 
 char _license[] SEC("license") = "GPL";
 
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__task {
+	struct bpf_iter_meta *meta;
+	struct task_struct *task;
+} __attribute__((preserve_access_index));
+
 SEC("iter/task")
 int dump_task(struct bpf_iter__task *ctx)
 {

tools/testing/selftests/bpf/progs/bpf_iter_test_kern4.c

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
+#define bpf_iter_meta bpf_iter_meta___not_used
+#define bpf_iter__bpf_map bpf_iter__bpf_map___not_used
 #include "vmlinux.h"
+#undef bpf_iter_meta
+#undef bpf_iter__bpf_map
 #include <bpf/bpf_helpers.h>
 
 char _license[] SEC("license") = "GPL";
 
+struct bpf_iter_meta {
+	struct seq_file *seq;
+	__u64 session_id;
+	__u64 seq_num;
+} __attribute__((preserve_access_index));
+
+struct bpf_iter__bpf_map {
+	struct bpf_iter_meta *meta;
+	struct bpf_map *map;
+} __attribute__((preserve_access_index));
+
 __u32 map1_id = 0, map2_id = 0;
 __u32 map1_accessed = 0, map2_accessed = 0;
 __u64 map1_seqnum = 0, map2_seqnum1 = 0, map2_seqnum2 = 0;