Build ebpf program from custom sources (.c / .h)

[spumer]

We want customize ebpf logic by outer rules. The best way is generate .c file and use it instead builtin.

This allow sqproxy generate ebpf-program by own rules (e.g plugins) and then pass generated sources to sqredirect.

The main reason is move reply logic from python to kernel. sqproxy can update data in buffers, kernel will use it to reply for a2s requests. This should be faster than C+NFQUEUE