lwip: refractor to esp specific counter

1. Add tcp debug counter
2. Refractor other ESP specific counter

components/lwip/core/stats.c

@@ -180,7 +180,7 @@ stats_display(void)
 }
 #endif /* LWIP_STATS_DISPLAY */
 
-#if ESP_STATS
+#if ESP_STATS_DROP
 void stats_display_esp(struct stats_esp *esp)
 {
   LWIP_PLATFORM_DIAG(("\nESP\n\t"));

components/lwip/core/tcp.c

@@ -906,6 +906,8 @@ tcp_slowtmr_start:
                                       " pcb->rto %"S16_F"\n",
                                       pcb->rtime, pcb->rto));
 
+          ESP_STATS_TCP_PCB(pcb);
+
           /* Double retransmission time-out unless we are trying to
            * connect to somebody (i.e., we are in SYN_SENT). */
           if (pcb->state != SYN_SENT) {

components/lwip/core/tcp_out.c

@@ -213,6 +213,7 @@ tcp_create_segment(struct tcp_pcb *pcb, struct pbuf *p, u8_t flags, u32_t seqno,
   TCPH_HDRLEN_FLAGS_SET(seg->tcphdr, (5 + optlen / 4), flags);
   /* wnd and chksum are set in tcp_output */
   seg->tcphdr->urgp = 0;
+
   return seg;
 }
 
@@ -1424,6 +1425,7 @@ tcp_rexmit(struct tcp_pcb *pcb)
   }
 #endif /* TCP_OVERSIZE */
 
+  ESP_STATS_TCP_PCB(pcb);
   ++pcb->nrtx;
 
   /* Don't take any rtt measurements after retransmitting. */