ospfd: convert uptime to epoch for ip ospf neigh

Currently, json output of show ip ospf neighbor commands are
having "uptime" in "17.515s" format.

uptime is converted into epoch format and added json attributes.

Supported commands:

```
show ip ospf vrf <vrf-id> neighbor json
show ip ospf vrf <VRFNAME> neighbor <neighbor-id> json
```

Sample ip ospf neighbor json output:

```
tor-21# show ip ospf vrf default neighbor swp1 json
{
  "6.0.0.9":[
    {
      "nbrState":"Full\/-",
      "nbrPriority":1,
      "converged":"Full",
      "role":"DROther",
      "upTimeInMsec":17515,
      "routerDeadIntervalTimerDueMsec":32482,
      "upTime":"17.515s",
      "deadTime":"32.482s",
      "ospfNeighUptimeEpoch":1691046764,
      "ospfNeighUptimeEpochStr":"Thu Aug  3 07:12:44 2023\n",
      "ifaceAddress":"6.0.0.9",
      "ifaceName":"swp1:6.0.0.17",
      "linkStateRetransmissionListCounter":0,
      "linkStateRequestListCounter":0,
      "databaseSummaryListCounter":0
    }
  ]
}
tor-21#
```

Ticket:#3541629

Issue:3541629

Testing: UT done

Signed-off-by: Sindhu Parvathi Gopinathan's <[email protected]>

ospfd/ospf_vty.c

@@ -4622,11 +4622,16 @@ static void show_ip_ospf_neighbour_brief(struct vty *vty,
 	struct timeval res = {.tv_sec = 0, .tv_usec = 0};
 	long time_val = 0;
 	char uptime[OSPF_TIME_DUMP_SIZE];
+	time_t epoch_tbuf = 0;
 
 	if (nbr->ts_last_progress.tv_sec || nbr->ts_last_progress.tv_usec)
 		time_val =
 			monotime_since(&nbr->ts_last_progress, &res) / 1000LL;
 
+	if (nbr->ts_last_progress.tv_sec)
+		epoch_tbuf = time(NULL) -
+			     (monotime(NULL) - (nbr->ts_last_progress.tv_sec));
+
 	if (use_json) {
 		char neigh_str[INET_ADDRSTRLEN];
 
@@ -4684,6 +4689,11 @@ static void show_ip_ospf_neighbour_brief(struct vty *vty,
 				json_neighbor, "deadTime",
 				ospf_timer_dump(nbr->t_inactivity, timebuf,
 						sizeof(timebuf)));
+			json_object_int_add(json_neighbor,
+					    "ospfNeighUptimeEpoch", epoch_tbuf);
+			json_object_string_add(json_neighbor,
+					       "ospfNeighUptimeEpochStr",
+					       ctime(&epoch_tbuf));
 		} else {
 			json_object_string_add(json_neighbor, "deadTimeMsecs",
 					       "inactive");