isisd: Show correct level information for `show isis interface detail json`

isisd: Show correct level information for `show isis interface detail json`

Having this configuration:

```
!
interface r1-eth0
 ip address 10.0.0.1/30
 ip router isis 1
 isis priority 44 level-1
 isis priority 88 level-2
 isis csnp-interval 90 level-1
 isis csnp-interval 99 level-2
 isis psnp-interval 70 level-1
 isis psnp-interval 50 level-2
 isis hello-interval level-1 120
 isis hello-interval level-2 150

!
interface r1-eth1
 ip address 10.0.0.10/30
 ip router isis 1
!
interface lo
 ip address 192.0.2.1/32
 ip router isis 1
 isis passive
!
router isis 1
net 49.0000.0000.0000.0001.00
 metric-style wide
```

Produces:

```
{
 "areas":[
   {
     "area":"1",
     "circuits":[
       {
         "circuit":2,
         "interface":{
           "name":"r1-eth0",
           "state":"Up",
           "is-passive":"active",
           "circuit-id":"0x2",
           "type":"lan",
           "level":"L1L2",
           "snpa":"6e28.9c92.da5e",
           "levels":[
             {
               "level":"L1",
               "metric":10,
               "active-neighbors":1,
               "hello-interval":120,
               "holddown":{
                 "count":10,
                 "pad":"yes"
               },
               "cnsp-interval":90,
               "psnp-interval":70,
               "lan":{
                 "priority":44,
                 "is-dis":"no"
               }
             },
             {
               "level":"L2",
               "metric":10,
               "active-neighbors":1,
               "hello-interval":120, <<<<<<<<<<<<<<<<<<
               "holddown":{
                 "count":10,
                 "pad":"yes"
               },
               "cnsp-interval":90, <<<<<<<<<<<<<<<<<<
               "psnp-interval":70, <<<<<<<<<<<<<<<<<<
               "lan":{
                 "priority":44, <<<<<<<<<<<<<<<<<<
                 "is-dis":"no"
               }
             }
           ],
...
```

Fixes: 9fee4d4c6038ef6b14e9f509d6b04d189660c4cd ("isisd: Add json to show isis interface command.")
Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>