+
+ /*
+ * Add encapsulation header.
+ *
+ * On exit, the transport header will be set to the start of the
+ * encapsulation header to be filled in by x->type->output and
+ * the mac header will be set to the nextheader (protocol for
+ * IPv4) field of the extension header directly preceding the
+ * encapsulation header, or in its absence, that of the top IP
+ * header. The value of the network header will always point
+ * to the top IP header while skb->data will point to the payload.
+ */