code cleanup

Define $ip_alias_name to make it easier to read the code.
update update_nf_conntrack_max && nf_conntrack_tcp_timeout_established after modules load

/proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established
and
/proc/sys/net/nf_conntrack_max

are empty by default, because conntrack module is not loaded, until we have apply iptables rules

So, we just need to update them after iptables commit (which load the conntrack modules)

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
ruleset_generate_rule: update all or nothing

And use 'warn' instead of 'die' if alias does not exists.
generate_nfqueue: code cleanup