Fix up ndis interaction with net80211

• make NDIS_DEBUG a sysctl
• default to IEEE80211_MODE_11B if the card doesnt tell us the channels
• dont mess with ic_des_chan when we assosciate
• Allow a directed scan by setting the ESSID before scanning (verified with wireshark). Hidden APs probably wouldnt have worked before.
• Grab the channel type and use it to look up the correct curchan for the scan results (mistakenly used 11B before)
• Fix memory leak in the ndis_scan_results

Tested by: matteo
Reviewed by: sam
Approved by: re (rwatson)