ipvs: stop tot_stats estimator only under CONFIG_SYSCTL

[ Upstream commit 9802d21e7a0b0d2167ef745edc1f4ea7a0fc6ea3 ]

The tot_stats estimator is started only when CONFIG_SYSCTL
is defined. But it is stopped without checking CONFIG_SYSCTL.
Fix the crash by moving ip_vs_stop_estimator into
ip_vs_control_net_cleanup_sysctl.

The change is needed after commit 14e405461e664b
("IPVS: Add __ip_vs_control_{init,cleanup}_sysctl()") from 2.6.39.

Reported-by: Jet Chen <jet.chen@intel.com>
Tested-by: Jet Chen <jet.chen@intel.com>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>