modules: hostap: Decrease supplicant thread stack size

Based on few tests, it was observed that WPA supplicant's maximum usage
for connection and disconnection is 4360.

This would save ~4K which is huge as we have a crunch for RAM.

This was missed when hostap was upstreamed from NCS.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>