iwlwifi: make data frame tracing optional

When tracing in iwlwifi, we get all data. Most of
the time, we don't need it, and it just takes up
a lot of extra space in the trace.

Make this optional by recording the data into two
separate trace events if it is needed. Without it,
record only the content of non-data and EAPOL TX
frames.

As a result, tracing without the data tracepoints
will record meta information including the 802.11
headers for all frames but will not record the
contents of data frames to reduce trace overhead.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>