Added the option PBUF_LINK_ENCAPSULATION_HLEN to allocate additional header space for TX on netifs requiring additional headers

src/include/lwip/opt.h

@@ -1189,6 +1189,14 @@
 #endif /* LWIP_HOOK_VLAN_SET */
 #endif
 
+/**
+ * PBUF_LINK_ENCAPSULATION_HLEN: the number of bytes that should be allocated
+ * for an additional encapsulation header before ethernet headers (e.g. 802.11)
+ */
+#ifndef PBUF_LINK_ENCAPSULATION_HLEN
+#define PBUF_LINK_ENCAPSULATION_HLEN    0
+#endif
+
 /**
  * PBUF_POOL_BUFSIZE: the size of each pbuf in the pbuf pool. The default is
  * designed to accommodate single full size TCP frame in one pbuf, including

src/include/lwip/pbuf.h

@@ -60,6 +60,7 @@ typedef enum {
   PBUF_TRANSPORT,
   PBUF_IP,
   PBUF_LINK,
+  PBUF_RAW_TX,
   PBUF_RAW
 } pbuf_layer;