mac80211: allow null chandef in tracing

mac80211: allow null chandef in tracing

commit 254d3dfe445f94a764e399ca12e04365ac9413ed upstream.

In TDLS channel-switch operations the chandef can sometimes be NULL.
Avoid an oops in the trace code for these cases and just print a
chandef full of zeros.

Fixes: a7a6bdd0670fe ("mac80211: introduce TDLS channel switch ops")
Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>