mac80211: tkip.c use kernel-provided infrastructure

Use kernel-provided bit rotation and unaligned access infrastructure rather
than opencoding it.

Some minor spacing adjustments as well.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Cc: "John W. Linville" <linville@tuxdriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>