selftests/bpf: A pro/epilogue test when the main prog jumps back to the 1st insn

This patch adds a pro/epilogue test when the main prog has a goto insn
that goes back to the very first instruction of the prog. It is
to test the correctness of the adjust_jmp_off(prog, 0, delta)
after the verifier has applied the prologue and/or epilogue patch.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20240829210833.388152-9-martin.lau@linux.dev


Signed-off-by: Alexei Starovoitov <ast@kernel.org>