[PATCH bpf-next] selftests/bpf: Fix compilation errors

[Feng Yang <yangfeng59949@163.com>]

From: Feng Yang <yangfeng@kylinos.cn>

If the CONFIG_NET_SCH_BPF configuration is not enabled,
the BPF test compilation will report the following error:
In file included from progs/bpf_qdisc_fq.c:39:
progs/bpf_qdisc_common.h:17:51: error: declaration of 'struct bpf_sk_buff_ptr' will not be visible outside of this function [-Werror,-Wvisibility]
   17 | void bpf_qdisc_skb_drop(struct sk_buff *p, struct bpf_sk_buff_ptr *to_free) __ksym;
      |                                                   ^
progs/bpf_qdisc_fq.c:309:14: error: declaration of 'struct bpf_sk_buff_ptr' will not be visible outside of this function [-Werror,-Wvisibility]
  309 |              struct bpf_sk_buff_ptr *to_free)
      |                     ^
progs/bpf_qdisc_fq.c:309:14: error: declaration of 'struct bpf_sk_buff_ptr' will not be visible outside of this function [-Werror,-Wvisibility]
progs/bpf_qdisc_fq.c:308:5: error: conflicting types for '____bpf_fq_enqueue'

Fixes: 11c701639ba9 ("selftests/bpf: Add a basic fifo qdisc test")
Signed-off-by: Feng Yang <yangfeng@kylinos.cn>
---
 tools/testing/selftests/bpf/progs/bpf_qdisc_common.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_common.h b/tools/testing/selftests/bpf/progs/bpf_qdisc_common.h
index 65a2c561c0bb..7e7f2fe04f22 100644
--- a/tools/testing/selftests/bpf/progs/bpf_qdisc_common.h
+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_common.h
@@ -12,6 +12,8 @@
 
 #define private(name) SEC(".data." #name) __hidden __attribute__((aligned(8)))
 
+struct bpf_sk_buff_ptr;
+
 u32 bpf_skb_get_hash(struct sk_buff *p) __ksym;
 void bpf_kfree_skb(struct sk_buff *p) __ksym;
 void bpf_qdisc_skb_drop(struct sk_buff *p, struct bpf_sk_buff_ptr *to_free) __ksym;
-- 
2.43.0