net: revert "sched classifier: make cgroup table local"

This reverts commit de6fb288.
Otherwise we got:

net/sched/cls_cgroup.c:106:29: error: static declaration of ‘net_cls_subsys’ follows non-static declaration
 static struct cgroup_subsys net_cls_subsys = {
                             ^
In file included from include/linux/cgroup.h:654:0,
                 from net/sched/cls_cgroup.c:18:
include/linux/cgroup_subsys.h:35:29: note: previous declaration of ‘net_cls_subsys’ was here
 SUBSYS(net_cls)
                             ^
make[2]: *** [net/sched/cls_cgroup.o] Error 1

Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>