bgpd:[GR] fix crash in print_bgp_vrfs json

When BGP is in warm boot and `show bgp vrfs json` is executed more than
once, bgpd crashes in print_bgp_vrfs. This is happening because of
JSON object is being added multiple times to the JSON array with out
allocating everytime in the for loop and when json is freed, it causes
the crash.

NOTE: This commit needs to be integrated with original commit 4af3b55

Ticket: #3861755

Testing:
Before the fix:

switch# show bgp vrfs json
Warning: connecting to bgpd...success!
{
.. <snippet>
}

switch# show bgp vrfs json
Warning: closing connection to bgpd because of an I/O error!
Warning: connecting to bgpd...failed!

After the fix:

BGP no longer crashes on `show bgp vrfs json` command and it works as
expected.

switch# show bgp vrfs json
{
  "vrfs":{
.. <snippet>
}

switch# show bgp vrfs json
{
  "vrfs":{
.. <snippet>
}
switch# show bgp vrfs json
{
  "vrfs":{
.. <snippet>
}
switch# show bgp vrfs json
{
  "vrfs":{
.. <snippet>
}

Signed-off-by: Karthikeya Venkat Muppalla <kmuppalla@nvidia.com>
Signed-off-by: Pooja Jagadeesh Doijode <pdoijode@nvidia.com>

Author: Karthikeya Venkat Muppalla

bgpd/bgp_vty.c

@@ -11227,11 +11227,11 @@ static void print_bgp_vrfs(struct bgp *bgp, struct vty *vty, json_object *json,
 			safi_t safi = SAFI_UNICAST;
 			struct graceful_restart_info *gr_info;
 			json_object *json_gr = NULL;
-			json_gr = json_object_new_object();
 			json_object *json_grs = NULL;
 			json_grs = json_object_new_array();
 
 			for (afi = AFI_IP; afi <= AFI_IP6; afi++) {
+				json_gr = json_object_new_object();
 				json_object_string_add(
 					json_gr, "addressFamily",
 					get_afi_safi_str(afi, safi, false));