Pause/Resume Wireless Scanning

[Sven <sr12 duke edu>]

Dan,

thanks for implementing optional scanning. the card still periodically
disassociates and cycles through the channels though. now it (initially)
happens every 10s or so, and watching iwconfig ath0 shows that it cycles
through the channels only once, with wireless scanning enabled it seems
to cycle through 2 times  (as before in previous NM).

Sven