bgpd: Fix the json output of show bgp all json to be in a valid format

bgpd: Fix the json output of show bgp all json to be in a valid format

In the json output of show bgp all json, the l2VpnEvpn afi-safi is
missing the 'routes' key making the json output format invalid.

Before Fix:
torm-11# sh bgp all json
{
<SNIP>....................
"l2VpnEvpn":{
{
  "27.0.0.15:2":{
    "rd":"27.0.0.15:2",
    "[4]:[03:44:38:39:ff:ff:01:00:00:01]:[32]:[27.0.0.15]":{
      "prefix":"[4]:[03:44:38:39:ff:ff:01:00:00:01]:[32]:[27.0.0.15]",
      "prefixLen":352,
      "paths":[
<SNIP>....................

After Fix:
torm-11# sh bgp all json
{
<SNIP>....................
"l2VpnEvpn":{
"routes":{
  "27.0.0.15:2":{
    "rd":"27.0.0.15:2",
    "[1]:[0]:[03:44:38:39:ff:ff:01:00:00:01]:[128]:[::]:[0]":{
      "prefix":"[1]:[0]:[03:44:38:39:ff:ff:01:00:00:01]:[128]:[::]:[0]",
      "prefixLen":352,
      "paths":[

Issue: 3472865
Ticket:#3472865

Signed-off-by: Rajasekar Raja <rajasekarr@nvidia.com>
(cherry picked from commit be66fa05c90bff66b7427e13ccb80bf8ecab2f38)