mac80211: add ieee80211_is_tx_data helper function

Add a helper function that checks if a frame is a data frame. Frames
with hardware encapsulation enabled are data frames.

Signed-off-by: Philipp Borgers <borgers@mi.fu-berlin.de>
Link: https://lore.kernel.org/r/20210519122019.92359-2-borgers@mi.fu-berlin.de


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