[PATCH bpf-next] bpf: test_run: Remove ipv6_bpf_stub usage

[Martin KaFai Lau <martin.lau@linux.dev>]

From: Martin KaFai Lau <martin.lau@kernel.org>

bpf_prog_test_run_skb() uses net->ipv6.ip6_null_entry for
BPF_PROG_TYPE_LWT_XMIT test runs.

It currently checks ipv6_bpf_stub before using ip6_null_entry.
ipv6_bpf_stub will be removed by the CONFIG_IPV6=m support removal
series posted at [1], so switch this check to ipv6_mod_enabled()
instead.

This change depends on that series [1]. Without it, CONFIG_IPV6=m is
still possible, and net->ipv6.ip6_null_entry remains NULL until
the IPv6 module is loaded.

[1] https://lore.kernel.org/netdev/20260320185649.5411-1-fmancera@suse.de/

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
 net/bpf/test_run.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 56bc8dc1e281..fb25184ed03b 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -1157,15 +1157,12 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 	}
 
 	if (prog->type == BPF_PROG_TYPE_LWT_XMIT) {
-		if (!ipv6_bpf_stub) {
-			pr_warn_once("Please test this program with the IPv6 module loaded\n");
+		if (!ipv6_mod_enabled()) {
+			pr_warn_once("Please test this program with IPv6 enabled kernel\n");
 			ret = -EOPNOTSUPP;
 			goto out;
 		}
 #if IS_ENABLED(CONFIG_IPV6)
-		/* For CONFIG_IPV6=n, ipv6_bpf_stub is NULL which is
-		 * handled by the above if statement.
-		 */
 		dst_hold(&net->ipv6.ip6_null_entry->dst);
 		skb_dst_set(skb, &net->ipv6.ip6_null_entry->dst);
 #endif
-- 
2.52.0