ospfd: Fix inconsistency in LSDB JSON output

ospfd: Fix inconsistency in LSDB JSON output

As it can be seen below, the LSDB JSON output varies depending
whether a filter option is specified or not (e.g. "adv-router",
"self-originate"):

> show ip ospf database router json
{
  "routerId":"3.3.3.3",
  "routerLinkStates":{
    "areas":{
      "0.0.0.0":[
        {
          "lsaAge":175,
          "options":"*|-|-|-|-|-|E|-",
          [snip]

> show ip ospf database router adv-router 2.2.2.2 json
{
  "routerId":"3.3.3.3",
  "Router Link States":{
    "0.0.0.0":{
      "2.2.2.2":{
        "lsaAge":193,
        "options":"*|-|-|-|-|-|E|-",
        [snip]

This inconsistency is undesirable since it makes this data harder to
consume programmatically. Also, in the second output, "Router Link
States" is used as a JSON key, which doesn't conform to our JSON
guidelines (JSON keys need to be camelCased).

Make the required changes to ensure the first output structure is used,
regardless if any output filter is used or not.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>