ipvs: Fix reuse connection if real server is dead

Expire cached connection for new TCP/SCTP connection if real
server is down. Otherwise, IPVS uses the dead server for the
reused connection, instead of a new working one.

Signed-off-by: Grzegorz Lyczba <grzegorz.lyczba@gmail.com>
Acked-by: Hans Schillstrom <hans@schillstrom.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>