fix compile warning

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
fix invalid memory access bug introduced by filter support patch

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
add function filter sample script into README.md

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
remove perf_event_enable/disable for tracepoints

It have been found that perf_event_enable/disable is not needed
after perf_event_create_kernel_counter called, so remove it.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
refactor kp_ftrace_profile_set_filter

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