First restore "all" and then "default"(and "dev") as for some ipv6
sysctls setting all can change the latter(forwarding, disable_ipv6)

e.g.:
 echo 1 > /proc/sys/net/ipv6/conf/default/disable_ipv6
 echo 0 > /proc/sys/net/ipv6/conf/all/disable_ipv6
 cat /proc/sys/net/ipv6/conf/default/disable_ipv6
0

As changing disable_ipv6 sysctl for some device may change mtu sysctl
do not optimize mtu's restore.
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Reviewed-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>