libbpf: Use available_filter_functions_addrs with multi-kprobes

Now that kernel provides a new available_filter_functions_addrs file
which can help us avoid the need to cross-validate
available_filter_functions and kallsyms, we can improve efficiency of
multi-attach kprobes. For example, on my device, the sample program [1]
of start time:

$ sudo ./funccount "tcp_*"

before   after
1.2s     1.0s

  [1]: https://github.com/JackieLiu1/ketones/tree/master/src/funccount

Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230705091209.3803873-2-liu.yun@linux.dev