fix(lwip): Fix send TCP data with two or more pbuf

internal gitlab: d3a48012

Author: wujiangang

VERSION

@@ -18,5 +18,5 @@ phy:
 
 gitlab:
  driver : 68fc7b06
- lwip : 84bab89d
+ lwip : 3267f12f
  mbedtls : 1d0dfd8f

lib/liblwip.a

@@ -461,6 +461,7 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
  return ERR_MEM;
  }
 
+#if !LWIP_NETIF_TX_SINGLE_PBUF
  /*
  * Phase 2: Chain a new pbuf to the end of pcb->unsent.
  *
@@ -510,6 +511,7 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
  pos += seglen;
  queuelen += pbuf_clen(concat_p);
  }
+#endif /* !LWIP_NETIF_TX_SINGLE_PBUF */
  } else {
 #if TCP_OVERSIZE
  LWIP_ASSERT("unsent_oversize mismatch (pcb->unsent is NULL)",