[PATCH] libertas: make scan result handling more flexible

- use a linked list for scan results
- age scan results
- pass bss_descriptors around instead of indexes into the scan table
- lock access to the scan results
- stop returning EAGAIN from SIOCGIWSCAN handler

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>