Staging/vt66*: kconfig, depends on WLAN

The vt665[56] drivers can be built when CONFIG_NET=n &
CONFIG_NETDEVICES=n or just when CONFIG_WLAN=n.
This leads to build failures.
Prevent this by making them depend on WLAN.

[This patch was lost in a dualing trees merge;
still needs to be re-applied.]

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>