a No-SNAT router subnets cannot overlap with VPN subnets becasue of the rotuer
advertisment.
This patch adds validations when changing the rotuer GW or addign an interface.
Also change the local endpoint port creation so this port will have a distingished
name and device id/owner and won't be queried by mistake.
Change-Id: I41faf97bae67ca85b38da3ade47894865eac8d51
3fd27427ae