wlcore: fix started_vifs calculation

wlcore configures different dwell times according to number
of active interfaces (in order to prevent hurting VO during
scan).

However, determining active vif only according to
bss_conf->idle is not explicit enough, and might result
in non-started vifs being counted as started as well
(e.g. unassociated sta during sta).

Fix it by checking for explicit conditions according
to the vif type.

Signed-off-by: Eliad Peller <eliad@wizery.com>