mac80211: don't use kerneldoc for ieee80211_add_rx_radiotap_header

Doing so creates warnings, but the function is internal and
not part of the 802.11 docbooks, so it from kerneldoc.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -103,7 +103,7 @@ ieee80211_rx_radiotap_len(struct ieee80211_local *local,
 	return len;
 }
 
-/**
+/*
  * ieee80211_add_rx_radiotap_header - add radiotap header
  *
  * add a radiotap header containing all the fields which the hardware provided.