hostap: Set frequency before enabling the network

Enabling a network would trigger a scan. Since frequency is being
set after enable_network, first scan is issued without any
specific frequency.

Signed-off-by: Ravi Dondaputi <ravi.dondaputi@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>