VR: Add simple port-forwarding for the NAT4 module (DNAT)

[sk4zuzu]

Description Add ability to statically forward ports in iptables with -j DNAT --to-destination.

Use case Simple, static alternative to both LBs and SDNAT.

Interface Changes

• [x] Something like ONEAPP_VNF_NAT4_PORT_FWD0 = 80:1.2.3.4:8080 , similar to ssh -L notation maybe? (TBD)
• [ ] Add a sound interface in Sunstone