iwlwifi: fix tracing when tx only is enabled

iwl_trace_data is somewhat confusing. It returns a bool
that tells if the payload of the skb should be added to
the tx_data event. If it returns false, then the payload
of the skb is added to the tx event.

The purpose is to be able to start tracing with
-e iwlwifi
and record non-data packets only which saves bandwidth.

Since EAPOLs are important, seldom and not real data
packet (despite being WiFi data packets), they are
included in tx event and thus iwl_trace_data returns false
on those. This last part was buggy, and because of that,
all the data packets were included in the tx event.

Fix that.

Fixes: 0c4cb731

 ("iwlwifi: tracing: decouple from mac80211")
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>