wlcore: increase scan dwell times if no activity

There's a limit on scan dwell times of max 30ms in order
to avoid degrading voip traffic which could be going on
while scanning. However these dwell times increase the
chance of missing out on nearby APs leading to partial
scan results. Allow configuration of longer dwell times
in case there no active interface (i.e. no STA associated
or AP up).

[Arik - count started vifs using an in-driver function]

[Fixed some new checkpatch warnings regarding comments in the
networking subsystem. -- Luca]

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