cls_cgroup: Fix crash on module unload

cls_cgroup: Fix crash on module unload

[ Upstream commit c00b2c9e79466d61979cd21af526cc6d5d0ee04f ]

Somewhere along the lines net_cls_subsys_id became a macro when
cls_cgroup is built as a module.  Not only did it make cls_cgroup
completely useless, it also causes it to crash on module unload.

This patch fixes this by removing that macro.

Thanks to Eric Dumazet for diagnosing this problem.

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>