mac80211: misc cleanups

This patch removes unneeded member (skbuff) from
ieee80211_ibss_add_sta() method in its declaration (in ieee80211_i.h)
and its callers (in rx.c and mlme.c)

This patch removes unneeded member from struct ieee80211_rx_data
in ieee80211_i.h.

(Originally posted as two patches. -- JWL)

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>