mac80211: allow null chandef in tracing

commit 254d3dfe 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: a7a6bdd0 ("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: Luis Henriques <luis.henriques@canonical.com>

net/mac80211/trace.h

@@ -33,10 +33,10 @@
 			__field(u32, center_freq1)					\
 			__field(u32, center_freq2)
 #define CHANDEF_ASSIGN(c)							\
-			__entry->control_freq = (c)->chan ? (c)->chan->center_freq : 0;	\
-			__entry->chan_width = (c)->width;				\
-			__entry->center_freq1 = (c)->center_freq1;			\
-			__entry->center_freq2 = (c)->center_freq2;
+			__entry->control_freq = (c) ? ((c)->chan ? (c)->chan->center_freq : 0) : 0;	\
+			__entry->chan_width = (c) ? (c)->width : 0;			\
+			__entry->center_freq1 = (c) ? (c)->center_freq1 : 0;		\
+			__entry->center_freq2 = (c) ? (c)->center_freq2 : 0;
 #define CHANDEF_PR_FMT	" control:%d MHz width:%d center: %d/%d MHz"
 #define CHANDEF_PR_ARG	__entry->control_freq, __entry->chan_width,			\
 			__entry->center_freq1, __entry->center_freq2