Merge branch 'cgroup-auto-detach'

Roman Gushchin says:

====================
This patchset implements a cgroup bpf auto-detachment functionality:
bpf programs are detached as soon as possible after removal of the
cgroup, without waiting for the release of all associated resources.

Patches 2 and 3 are required to implement a corresponding kselftest
in patch 4.

v5:
  1) rebase

v4:
  1) release cgroup bpf data using a workqueue
  2) add test_cgroup_attach to .gitignore

v3:
  1) some minor changes and typo fixes

v2:
  1) removed a bogus check in patch 4
  2) moved buf[len] = 0 in patch 2
====================

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