Really doesn't need to be defined four times.

Also, while at it, remove a useless macro (IEEE80211_ALIGN32_PAD)
and a function prototype for a function we don't actually have
(ieee80211_set_compression.)
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>