Merged in antmerlino/nuttx/sixlowpan-d_buf-fix (pull request #795)

net/sixlowpan: Record and restore d_buf on entry/exit of sixlowpan_input. This avoids an issue where d_buf gets set to NULL by sixlowpan, and then is used by forwarding logic from another network interface before getting set back to the drivers internal b

Approved-by: GregoryN <gnutt@nuttx.org>

net/sixlowpan/sixlowpan_input.c

@@ -716,9 +716,16 @@ int sixlowpan_input(FAR struct radio_driver_s *radio,
                     FAR struct iob_s *framelist,  FAR const void *metadata)
 {
   int ret = -EINVAL;
+  uint8_t *d_buf_backup;
 
   DEBUGASSERT(radio != NULL && framelist != NULL);
 
+  /* Sixlowpan modifies the d_buf to process fragments using reassembly buffers.
+   * Save the value of d_buf on entry and set it back before returning
+   */
+
+  d_buf_backup = radio->r_dev.d_buf;
+
   /* Verify that an frame has been provided. */
 
   while (framelist != NULL)
@@ -856,6 +863,10 @@ drop:
         }
     }
 
+  /* Restore the d_buf back to it's original state */
+
+  radio->r_dev.d_buf = d_buf_backup;
+
   return ret;
 }