specify how to reenable padding

Arti has a "dormant mode" which means that it might need to reenable channel padding after hving disabled it.

How to do this, paarticularly in the face of possibly changing consensus parameters, is an edge case.

padding-spec.txt

@@ -266,6 +266,16 @@ Table of Contents
   immediately after sending their NETINFO cell.  Recipients SHOULD, however,
   accept padding negotiation messages at any time.
 
+  If a client which previously negotiated reduced, or disabled, padding, and
+  wishes to re-enable default padding (ie padding according to the consensus
+  parameters), it SHOULD send CELL_PADDING_NEGOTIATE START with zero in the
+  ito_low_ms and ito_high_ms fields.  (It therefore SHOULD NOT copy the values
+  from its own established consensus into the CELL_PADDING_NEGOTIATE cell.)
+  This avoids the client needing to send updated padding negotiations if the
+  consensus parameters should change.  The recipient's clamping of the timing
+  parameters will cause the recipient to use its notion of the consensus
+  parameters.
+
   Clients and bridges MUST reject padding negotiation messages from relays,
   and close the channel if they receive one.