selftests/bpf: Fix kprobe_multi test.

When compiler emits endbr insn the function address could
be different than what bpf_get_func_ip() reports.
This is a short term workaround.
bpf_get_func_ip() will be fixed later.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Alexei Starovoitov

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

@@ -36,13 +36,15 @@ __u64 kretprobe_test6_result = 0;
 __u64 kretprobe_test7_result = 0;
 __u64 kretprobe_test8_result = 0;
 
+extern bool CONFIG_X86_KERNEL_IBT __kconfig __weak;
+
 static void kprobe_multi_check(void *ctx, bool is_return)
 {
 	if (bpf_get_current_pid_tgid() >> 32 != pid)
 		return;
 
 	__u64 cookie = test_cookie ? bpf_get_attach_cookie(ctx) : 0;
-	__u64 addr = bpf_get_func_ip(ctx);
+	__u64 addr = bpf_get_func_ip(ctx) - (CONFIG_X86_KERNEL_IBT ? 4 : 0);
 
 #define SET(__var, __addr, __cookie) ({			\
 	if (((const void *) addr == __addr) &&		\