[PATCH] fix NET_RADIO=n, IEEE80211=y compile

This patch fixes the following compile error with CONFIG_NET_RADIO=n and
CONFIG_IEEE80211=y:

  LD      .tmp_vmlinux1
net/built-in.o: In function `ieee80211_rx':
: undefined reference to `wireless_spy_update'
make: *** [.tmp_vmlinux1] Error 1

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>