libertas: Fix ethtool reporting no WOL options supported if WOL is not already active

This patch fixes the libertas driver incorrectly reporting that Wake-on-LAN
is not supported if Wake-on-LAN is currently disabled.

Signed-off-by: Sascha Silbe <sascha-pgp@silbe.org>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>