samples/bpf: Add openat2() enter/exit tracepoint to syscall_tp sample

Commit fe330089

("samples: bpf: fix syscall_tp due to unused syscall")
added openat() syscall tracepoints. This patch adds support for
openat2() as well.

Signed-off-by: Rong Tao <rongtao@cestc.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/tencent_9381CB1A158ED7ADD12C4406034E21A3AC07@qq.com