[PATCH] zd1211rw: Fixes radiotap header

There has been a problem in the radiotap header. Monitor mode
works now with tcpdump 3.94 + libpcap 0.9.4. ethereal 0.99.0 +
libpcap 0.9.4 is broken, because it doesn't find the right offset
for the IEEE 802.11 header.

Signed-off-by: Ulrich Kunitz <kune@deine-taler.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>