Use channel_is_client() accessor in channelpadding.c.

Also, allow channel_is_client() to take a const channel.

src/or/channel.c

@@ -4075,7 +4075,7 @@ channel_mark_bad_for_new_circs(channel_t *chan)
  */
 
 int
-channel_is_client(channel_t *chan)
+channel_is_client(const channel_t *chan)
 {
   tor_assert(chan);
 

src/or/channel.h

@@ -666,7 +666,7 @@ int channel_is_bad_for_new_circs(channel_t *chan);
 void channel_mark_bad_for_new_circs(channel_t *chan);
 int channel_is_canonical(channel_t *chan);
 int channel_is_canonical_is_reliable(channel_t *chan);
-int channel_is_client(channel_t *chan);
+int channel_is_client(const channel_t *chan);
 int channel_is_local(channel_t *chan);
 int channel_is_incoming(channel_t *chan);
 int channel_is_outgoing(channel_t *chan);

src/or/channelpadding.c

@@ -66,7 +66,7 @@ static int consensus_nf_pad_relays;
  *  its a client, use that. Then finally verify in the consensus).
  */
 #define CHANNEL_IS_CLIENT(chan, options) \
-  (!public_server_mode((options)) || (chan)->is_client || \
+  (!public_server_mode((options)) || channel_is_client(chan) || \
       !connection_or_digest_is_known_relay((chan)->identity_digest))
 
 /**