wireless: fix for CONFIG_NL80211=n

Add empty function for case of CONFIG_NL80211=n:

net/wireless/scan.c:35: error: implicit declaration of function 'nl80211_send_scan_aborted'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>