isisd: show isis route .. json adds the algorithm value

isisd: show isis route .. json adds the algorithm value

When walking over all the flex-algorithm routes, it is
difficult to know which route is associated to which
algorithm: add "algorithm" attribute to the json object.

Output example:

> ubuntu2004(config-router)# do show isis route algorithm  json
> [
>   {
>     "area":"1",
>     "algorithm":128,
>     "level-1":{
>      ]
>    },
>    "level-2":{
>      "area":"1"
>    },
>    "vrf_id":0
>  },
>  {
>    "area":"1",
>    "algorithm":129,
>    "level-1":{
>      "area":"1",

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>