bpf: Fix bpf_session_cookie BTF_ID in special_kfunc_set list

The bpf_session_cookie is unavailable for !CONFIG_FPROBE as reported
by Sebastian [1].

To fix that we remove CONFIG_FPROBE ifdef for session kfuncs, which
is fine, because there's filter for session programs.

Then based on bpf_trace.o dependency:
  obj-$(CONFIG_BPF_EVENTS) += bpf_trace.o

we add bpf_session_cookie BTF_ID in special_kfunc_set list dependency
on CONFIG_BPF_EVENTS.

[1] https://lore.kernel.org/bpf/20240531071557.MvfIqkn7@linutronix.de/T/#m71c6d5ec71db2967288cb79acedc15cc5dbfeec5Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Fixes: 5c919ace ("bpf: Add support for kprobe session cookie")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20240531194500.2967187-1-jolsa@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -11128,7 +11128,11 @@ BTF_ID(func, bpf_iter_css_task_new)
 #else
 BTF_ID_UNUSED
 #endif
+#ifdef CONFIG_BPF_EVENTS
 BTF_ID(func, bpf_session_cookie)
+#else
+BTF_ID_UNUSED
+#endif
 
 static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
 {

kernel/trace/bpf_trace.c

@@ -3517,7 +3517,6 @@ static u64 bpf_uprobe_multi_entry_ip(struct bpf_run_ctx *ctx)
 }
 #endif /* CONFIG_UPROBES */
 
-#ifdef CONFIG_FPROBE
 __bpf_kfunc_start_defs();
 
 __bpf_kfunc bool bpf_session_is_return(void)
@@ -3566,4 +3565,3 @@ static int __init bpf_kprobe_multi_kfuncs_init(void)
 }
 
 late_initcall(bpf_kprobe_multi_kfuncs_init);
-#endif