ipvs: add assured state for conn templates

cp->state was not used for templates. Add support for state bits
and for the first "assured" bit which indicates that some
connection controlled by this template was established or assured
by the real server. In a followup patch we will use it to drop
templates under SYN attack.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>