staging: r8712u: Merging Realtek's latest (v2.6.6). Tx aggregation.

Tx Aggregation (CONFIG_R8712_TX_AGGR, known as CONFIG_USB_TX_AGGR in the
Realtek tarball) is now added.

However, its tests have not been successful! The default in the Realtek
tarball is to not build it -- and the Release Notes does not seem to list this
as a feature. I have tested the driver with and without this feature; the
former does not successfully associate when WPA2 is used.

Signed-off-by: Ali Bahar <ali@internetDog.org>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>