zebra: Free Zebra client resources

Memory leaks started flowing:

```
AddressSanitizer Topotests Part 0:  15 KB -> 283 KB
AddressSanitizer Topotests Part 1:  1 KB -> 495 KB
AddressSanitizer Topotests Part 2:  13 KB -> 478 KB
AddressSanitizer Topotests Part 3:  39 KB -> 213 KB
AddressSanitizer Topotests Part 4:  30 KB -> 836 KB
AddressSanitizer Topotests Part 5:  0 bytes -> 356 KB
AddressSanitizer Topotests Part 6:  86 KB -> 783 KB
AddressSanitizer Topotests Part 7:  0 bytes -> 354 KB
AddressSanitizer Topotests Part 8:  0 bytes -> 62 KB
AddressSanitizer Topotests Part 9:  408 KB -> 518 KB
```

```
Direct leak of 3584 byte(s) in 1 object(s) allocated from:
    #0 0x7f1957b02d28 in __interceptor_calloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xded28)
    #1 0x559895c55df0 in qcalloc lib/memory.c:105
    FRRouting#2 0x559895bc1cdf in zserv_client_create zebra/zserv.c:743
    FRRouting#3 0x559895bc1cdf in zserv_accept zebra/zserv.c:880
    FRRouting#4 0x559895cf3438 in event_call lib/event.c:1995
    FRRouting#5 0x559895c3901c in frr_run lib/libfrr.c:1213
    FRRouting#6 0x559895a698f1 in main zebra/main.c:472
    FRRouting#7 0x7f195635ec86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21c86)
```

Fixes b20acd0 ("bgpd: Use synchronous way to get labels from Zebra")

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

zebra/zserv.c

@@ -582,30 +582,27 @@ static void zserv_client_free(struct zserv *client)
 
 	/* Close file descriptor. */
 	if (client->sock) {
-		unsigned long nroutes;
-		unsigned long nnhgs;
+		unsigned long nroutes = 0;
+		unsigned long nnhgs = 0;
 
 		close(client->sock);
 
-		/* If this is a synchronous BGP Zebra client for label/table
-		 * manager, then ignore it. It's not GR-aware, and causes GR to
-		 * be skipped for the session_id == 0 (asynchronous).
-		 */
-		if (client->proto == ZEBRA_ROUTE_BGP && client->session_id == 1)
-			return;
-
 		if (DYNAMIC_CLIENT_GR_DISABLED(client)) {
-			zebra_mpls_client_cleanup_vrf_label(client->proto);
+			if (!client->synchronous) {
+				zebra_mpls_client_cleanup_vrf_label(
+					client->proto);
 
-			nroutes = rib_score_proto(client->proto,
-						  client->instance);
+				nroutes = rib_score_proto(client->proto,
+							  client->instance);
+			}
 			zlog_notice(
 				"client %d disconnected %lu %s routes removed from the rib",
 				client->sock, nroutes,
 				zebra_route_string(client->proto));
 
 			/* Not worrying about instance for now */
-			nnhgs = zebra_nhg_score_proto(client->proto);
+			if (!client->synchronous)
+				nnhgs = zebra_nhg_score_proto(client->proto);
 			zlog_notice(
 				"client %d disconnected %lu %s nhgs removed from the rib",
 				client->sock, nnhgs,