Merge branch 'Refactor verifier prune and jump point handling'

Andrii Nakryiko says:

====================

Disentangle prune and jump points in BPF verifier code. They are conceptually
independent but currently coupled together. This small patch set refactors
related code and make it possible to have some instruction marked as pruning
or jump point independently.

Besides just conceptual cleanliness, this allows to remove unnecessary jump
points (saving a tiny bit of performance and memory usage, potentially), and
even more importantly it allows for clean extension of special pruning points,
similarly to how it's done for BPF_FUNC_timer_set_callback. This will be used
by future patches implementing open-coded BPF iterators.

v1->v2:
  - clarified path #3 commit message and a comment in the code (John);
  - added back mark_jmp_point() to right after subprog call to record
    non-linear implicit jump from BPF_EXIT to right after CALL <subprog>.
====================

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