selftests: bpf: Add missing symbol declarations to common header

Fix implicit function declaration errors in bpf_qdisc_xxx.c by adding
the required kernel symbol declarations to the shared header file
bpf_qdisc_common.h. This ensures all qdisc BPF programs can properly
resolve these kernel functions.

The added declarations include:
- bpf_qdisc_skb_drop
- bpf_qdisc_bstats_update
- bpf_kfree_skb
- bpf_skb_get_hash
- bpf_qdisc_watchdog_schedule

Using a common header prevents duplication and ensures consistency
across different qdisc implementations.

Signed-off-by: Yuan Chen <[email protected]>

Author: chenyuan0001

tools/testing/selftests/bpf/progs/bpf_qdisc_common.h

@@ -14,6 +14,15 @@
 
 struct bpf_sk_buff_ptr;
 
+extern void bpf_qdisc_skb_drop(struct sk_buff *skb,
+			       struct bpf_sk_buff_ptr *to_free_list) __ksym;
+extern void bpf_qdisc_bstats_update(struct Qdisc *sch,
+				    const struct sk_buff *skb) __ksym;
+extern void bpf_kfree_skb(struct sk_buff *skb) __ksym;
+extern u32 bpf_skb_get_hash(struct sk_buff *skb) __ksym;
+extern void bpf_qdisc_watchdog_schedule(struct Qdisc *sch, u64 expire,
+					u64 delta_ns) __ksym;
+
 static struct qdisc_skb_cb *qdisc_skb_cb(const struct sk_buff *skb)
 {
 	return (struct qdisc_skb_cb *)skb->cb;