nat: T4367: Move nat rules from /tmp to /run/nftables_nat.conf

[sever-sever]

Change Summary

Move nftables nat configuration from /tmp to /run
As we have for other services like firewall, conntrack
Don't remove the config file '/run/nftables_nat.conf' after commit

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://phabricator.vyos.net/T4367

Component(s) name

nat

Proposed changes

How to test

set nat destination rule 100 destination port '2222'
set nat destination rule 100 inbound-interface 'eth0'
set nat destination rule 100 protocol 'tcp'
set nat destination rule 100 translation address '192.0.2.2'
set nat destination rule 100 translation port '22'

Expect file /run/nftables_nat.conf

vyos@r14# cat /run/nftables_nat.conf 
#!/usr/sbin/nft -f


# Start with clean SNAT and DNAT chains
flush chain ip nat PREROUTING
flush chain ip nat POSTROUTING
add chain ip raw NAT_CONNTRACK
add rule ip raw NAT_CONNTRACK counter accept
add rule ip raw PREROUTING position 16    counter jump VYOS_CT_HELPER
add rule ip raw OUTPUT     position 21    counter jump VYOS_CT_HELPER
add rule ip raw PREROUTING position 18 counter jump NAT_CONNTRACK
add rule ip raw OUTPUT     position 23 counter jump NAT_CONNTRACK

#
# Destination NAT rules build up here
#
add rule ip nat PREROUTING counter jump VYOS_PRE_DNAT_HOOK

add rule ip nat PREROUTING iifname "eth0" ip protocol tcp tcp dport { 2222 } counter dnat to 192.0.2.2:22 comment "DST-NAT-100"

#
# Source NAT rules build up here
#
add rule ip nat POSTROUTING counter jump VYOS_PRE_SNAT_HOOK
[edit]
vyos@r14# 

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly