selftests/bpf: validate jit behaviour for tail calls

selftests/bpf: validate jit behaviour for tail calls

A program calling sub-program which does a tail call.
The idea is to verify instructions generated by jit for tail calls:
- in program and sub-program prologues;
- for subprogram call instruction;
- for tail call itself.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240820102357.3372779-9-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>