Reintroduce l3 router/gateway settings in l3 agent

This partially reverts commits f37dc6e037450a1c6dd0d20e05f99185efa6124f, e969a6f69eefc722c6fcd5d41ddbd6c30d36ce5b

Issue rcbops/chef-cookbooks#933
Merge pull request #138 from claco/issue-933

Merged automatically by jenkins after successful build test