ipvs: Store ipvs not net in struct ip_vs_sync_thread_data

In practice struct netns_ipvs is as meaningful as struct net and more
useful as it holds the ipvs specific data.  So store a pointer to
struct netns_ipvs.

Update the accesses of tinfo->net to access tinfo->ipvs->net instead.

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>