airo: sanitize BSSListRid handling

Stop byteswap-in-place in readBSSListRid(), annotate the sucker.
BTW, that had immediately found a bug - another codepath fetching
the same struct from card did _not_ byteswap, but used ->dBm the
same as everything else - host-endian.  Fix in the next patch...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: John W. Linville <linville@tuxdriver.com>