selinux: enable setting security context in cgroup

selinux: enable setting security context in cgroup

Orabug: 21295765

cgroup uses kernfs that has 'security.*' setxattr handler. But setxattr
with 'security.selinux' name returns EOPNOTSUPP, i.e. SBLABEL_MNT
not set on the cgroup filesystem.

Fix it by adding 'cgroup' type to genfs special handling list.

Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Guangyu Sun <guangyu.sun@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>