s390/config: Enable config options for Docker

The following config options are required/recommended for running Docker:

 Networking:

 - CONFIG_NF_NAT_MASQUERADE_IPV4=m
 - CONFIG_NF_NAT_MASQUERADE_IPV6=m
 - CONFIG_IPVLAN=m
 - CGROUP_NET_PRIO=y

 Storage drivers:

 - CONFIG_DM_THIN_PROVISIONING=m
 - CONFIG_OVERLAY_FS=m

 Scheduling:

 - CONFIG_FAIR_GROUP_SCHED=y
 - CONFIG_CFS_BANDWIDTH=y

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>