Added pbuf_ref_chain() which increases ref count of all pbufs in a chain.

src/core/pbuf.c

@@ -555,6 +555,20 @@ pbuf_ref(struct pbuf *p)
   }
   ++(p->ref);
 }
+
+/*------------------------------------------------------------------------------
+/* pbuf_ref_chain():
+ *
+ * Increments the reference count of all pbufs in a chain.
+ */
+void
+pbuf_ref_chain(struct pbuf *p)
+{
+  while (p != NULL) {
+    p->ref++;
+    p=p->next;
+  }
+}
 /*-----------------------------------------------------------------------------------*/
 /* pbuf_chain():
  *

src/include/lwip/pbuf.h

@@ -100,7 +100,7 @@ void pbuf_init(void);
                 prepended by allocating another pbuf and chain in to
                 the front of the ROM pbuf.
 
-   * PBUF_ROOL: the pbuf is allocated as a pbuf chain, with pbufs from
+   * PBUF_POOL: the pbuf is allocated as a pbuf chain, with pbufs from
                 the pbuf pool that is allocated during pbuf_init().  */
 struct pbuf *pbuf_alloc(pbuf_layer l, u16_t size, pbuf_flag flag);
 
@@ -123,7 +123,7 @@ u8_t pbuf_header(struct pbuf *p, s16_t header_size);
    Increments the reference count of the pbuf p.
  */
 void pbuf_ref(struct pbuf *p);
-
+void pbuf_ref_chain(struct pbuf *p);
 /* pbuf_free():
 
    Decrements the reference count and deallocates the pbuf if the