Porting Zebra fpm backpressure to dplane_fpm_sonic

Apply the following patch to dplane_fpm_sonic:
* Zebra fpm backpressure (FRRouting/frr#16220)

Signed-off-by: cscarpitta <cscarpit@cisco.com>

src/sonic-frr/dplane_fpm_sonic/dplane_fpm_sonic.c

@@ -2172,6 +2172,25 @@ static int fpm_nl_process(struct zebra_dplane_provider *prov)
 
 	fnc = dplane_provider_get_data(prov);
 	limit = dplane_provider_get_work_limit(prov);
+
+	frr_with_mutex (&fnc->ctxqueue_mutex) {
+		cur_queue = dplane_ctx_queue_count(&fnc->ctxqueue);
+	}
+
+	if (cur_queue >= (uint64_t)limit) {
+		if (IS_ZEBRA_DEBUG_FPM)
+			zlog_debug("%s: Already at a limit(%" PRIu64
+				   ") of internal work, hold off",
+				   __func__, cur_queue);
+		limit = 0;
+	} else {
+		if (IS_ZEBRA_DEBUG_FPM)
+			zlog_debug("%s: current queue is %" PRIu64
+				   ", limiting to lesser amount of %" PRIu64,•
+				   __func__, cur_queue, limit - cur_queue);
+		limit -= cur_queue;
+	}
+
 	for (counter = 0; counter < limit; counter++) {
 		ctx = dplane_provider_dequeue_in_ctx(prov);
 		if (ctx == NULL)