mac80211: adding 802.11n definitions in ieee80211.h

This patch adds several structs and definitions to ieee80211.h
to support 802.11n draft specifications.
As 802.11n depends on and extends the 802.11e standard in several issues,
there are also several definitions that belong to 802.11e.

Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>