+
+/* Modify the TCI field of 'packet'. If a VLAN tag is not present, one
+ * is added with the TCI field set to 'tci'. If a VLAN tag is present,
+ * then 'mask' bits are cleared before 'tci' is logically OR'd into the
+ * TCI field.
+ *
+ * Note that the function does not ensure that 'tci' does not affect
+ * bits outside of 'mask'.
+ */