mm: memcontrol: cleanup css_reset callback

- Do not take memcg_limit_mutex for resetting limits - the cgroup cannot
  be altered from userspace anymore, so no need to protect them.

- Use plain page_counter_limit() for resetting ->memory and ->memsw
  limits instead of mem_cgrouop_resize_* helpers - we enlarge the limits,
  so no need in special handling.

- Reset ->swap and ->tcpmem limits as well.

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>