Allow setting of openbmc defaul gateway with rspconfig command

[gurevichmark]

Based on discussion with Ratan on Slack:
https://ibm-systems-power.slack.com/archives/C0Q6TQP5Z/p1542385783338800

Seems like setting gateway value inside the network object is of no use.
We should instead set default gateway object.

[whowutwut]

@gurevichmark could you do a quick summary of what was addressed since not everyone would be able to read that slack channel..

OpenBMC will be implementing Redfish support, so the issue that we brought up will be addressed on that implementation rather than creating a change in the existing API, causing a big migration effort based on the firmware levels installed on the server.

[zet809]

Since it is very near the 2.14.5 release,(DCUT will be this friday), I'd like to move this issue to 2.15 and as @whowutwut mentioned, maybe implement in RedFish support.
What is your idea?

[gurevichmark]

@zet809 @whowutwut
Yes, according to Ratan, nothing will be changed in the current level of FW, they will do it in RedFish.

But our current implementation is not correct - changing the Gateway attribute inside the network object does not do anything.

"/xyz/openbmc_project/network/eth0/ipv4/9766662b": {
      "Address": "10.5.16.101",
      "Gateway": "10.0.0.105",
      "Origin": "xyz.openbmc_project.Network.IP.AddressOrigin.Static",
      "PrefixLength": 8,
      "Type": "xyz.openbmc_project.Network.IP.Protocol.IPv4"
    },

We need to change our rspconfig gateway= command to change the DefaultGateway attribute inside the network config object:

"data": {
    "/xyz/openbmc_project/network/config": {
      "DefaultGateway": "10.0.0.101",
      "HostName": "f5u16-bmc"
    }

This issue is to make changes to rspconfig command to allow display and modification of DefaultGateway attribute.