wlcore: fix link count in single-link-PSM optimization

commit 144614f3eebd7d only allowed a single active link when
turning on the optimization, ignoring the fact that an AP has two
additional global links.
Use 3 links as an indication for a single active link. Use the
FW PSM bits to verify the extra active link belongs to the AP role.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>