wifi: iwlwifi: refactor RX tracing

wifi: iwlwifi: refactor RX tracing

When there's not going to be any data in the data event, we
don't need to add it at all (unlike the TX version, it has
no data at all.)

Also combine the tracing into a separate inline so we only
call iwl_rx_trace_len() once, which also simplifies things,
and lets us have a single place to later add other checks.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20231207044813.13325a4848d2.Ic9e7d794fc4aebfe5ac5136b539ee62789f210f3@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>