fix the crash when tracing large events

Now ktap support trace bigger much events number, for example:
	trace probe:one_big_dso:* { }

Many big dso contains 20K symbols or more, ktap must need to support it.

To support this, kdebug.probe_by_id interface changed, don't pass string
anymore, use userspace memory pointer as first argument: struct eventdef_info.
	struct eventdef_info {
		int nr;
		int *id_arr;
		char *filter;
	};

It would be possible to embed this eventdef_info info trunk file in future.

Tested with nodejs, a compiled node process contains 17674 symbols.
(Another bug was found when test node, node coredump when using ktap script:
	trace probe:node:* {}
)

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
add documentation note for ftrace:function event

kernel must be newer than 3.3, then can use ftrace:function tracepoint in ktap.

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>