net: wireless: bcmdhd: adding boundary check in SWC gscan config

Since there's no boundary checking while looping NL structures, it could
corrupt kernel memory heap and leave room for security vulnerability
issue.
The proposed fix is adding a new NL attribute indicating how many SWC
bssids included. and it bounds NL iteration not to overwrite the
buffer.

Signed-off-by: Insun Song <insun.song@broadcom.com>
Bug: 34973477
Change-Id: I03e079b6054b930487230ca313bb96a7f9e63e64