ipvs: Cache ipvs in ip_vs_genl_set_cmd

Compute ipvs early in ip_vs_genl_set_cmd and use the cached value to
access ipvs->sync_state.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>