hostap: Add mode check for disconnect

This way we reject disconnect in AP mode and ap disable in STA mode,
though both have same functionality we treat them differently to keep
it clean.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>