hostap: kconfig: let entry be a menuconfig

wpa_supplicant has a lot of entries, and it appears in the top-level menu.
Let it be a menuconfig, so that it gets its own menu page with
all the options, instead of expanding in the top-level menu when
selected.

Signed-off-by: Emanuele Di Santo <emdi@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>