Add page(s) for libbpf helper-functions

[dylandreimerink]

LibBPF consists of a userspace and eBPF library. The eBPF library has numerous useful types and macros that are frequently used when building eBPF programs. It would be nice to add these to the docs, show how and why they are used.

• https://elixir.bootlin.com/linux/v6.8-rc4/source/tools/lib/bpf/bpf_helpers.h
• https://elixir.bootlin.com/linux/v6.8-rc4/source/tools/lib/bpf/bpf_core_read.h
• https://elixir.bootlin.com/linux/v6.8-rc4/source/tools/lib/bpf/bpf_endian.h
• https://elixir.bootlin.com/linux/v6.8-rc4/source/tools/lib/bpf/bpf_tracing.h