wifi: iwlwifi: tracing: fix condition to allocate buf1

There's no need to allocate buf1 if we're not going to
write anything to it, and the condition for writing is
(correctly) "hdr_len > 0 && !iwl_trace_data()". Also
allocate the event space only under the same condition.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240512152312.a11e6490d053.Ie090beea70d2f271bb22c9b0e287dbd342fb2a96@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>