selftests/bpf: Allow building bpf tests with CONFIG_XFRM_INTERFACE=[m|n]

It is useful to use vmlinux.h in the xfrm_info test like other kfunc
tests do.  In particular, it is common for kfunc bpf prog that requires
to use other core kernel structures in vmlinux.h

Although vmlinux.h is preferred, it needs a ___local flavor of
struct bpf_xfrm_info in order to build the bpf selftests
when CONFIG_XFRM_INTERFACE=[m|n].

Cc: Eyal Birger <eyal.birger@gmail.com>
Fixes: 90a3a05 ("selftests/bpf: add xfrm_info tests")
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20221206193554.1059757-1-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Martin KaFai Lau

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

@@ -3,26 +3,31 @@
 #include "bpf_tracing_net.h"
 #include <bpf/bpf_helpers.h>
 
+struct bpf_xfrm_info___local {
+	u32 if_id;
+	int link;
+} __attribute__((preserve_access_index));
+
 __u32 req_if_id;
 __u32 resp_if_id;
 
 int bpf_skb_set_xfrm_info(struct __sk_buff *skb_ctx,
-			  const struct bpf_xfrm_info *from) __ksym;
+			  const struct bpf_xfrm_info___local *from) __ksym;
 int bpf_skb_get_xfrm_info(struct __sk_buff *skb_ctx,
-			  struct bpf_xfrm_info *to) __ksym;
+			  struct bpf_xfrm_info___local *to) __ksym;
 
 SEC("tc")
 int set_xfrm_info(struct __sk_buff *skb)
 {
-	struct bpf_xfrm_info info = { .if_id = req_if_id };
+	struct bpf_xfrm_info___local info = { .if_id = req_if_id };
 
 	return bpf_skb_set_xfrm_info(skb, &info) ? TC_ACT_SHOT : TC_ACT_UNSPEC;
 }
 
 SEC("tc")
 int get_xfrm_info(struct __sk_buff *skb)
 {
-	struct bpf_xfrm_info info = {};
+	struct bpf_xfrm_info___local info = {};
 
 	if (bpf_skb_get_xfrm_info(skb, &info) < 0)
 		return TC_ACT_SHOT;