[PATCH] WE-21 support (core API)

This is version 21 of the Wireless Extensions. Changelog :
	o finishes migrating the ESSID API (remove the +1)
	o netdev->get_wireless_stats is no more
	o long/short retry

This is a redacted version of a patch originally submitted by Jean
Tourrilhes.  I removed most of the additions, in order to minimize
future support requirements for nl80211 (or other WE successor).

CC: Jean Tourrilhes <jt@hpl.hp.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>