ipvs: avoid kmem_cache_zalloc in ip_vs_conn_new

We have many fields to set and few to reset,
use kmem_cache_alloc instead to save some cycles.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off by: Hans Schillstrom <hans@schillstrom.com>
Signed-off-by: Simon Horman <horms@verge.net.au>