hostapd: Fix interfaces.iface initialization

hostapd: Fix interfaces.iface initialization

Set all the interfaces.iface pointers to NULL after the allocation of
that memory block for cases those pointers are accessed during each of
the interfaces initialization process (hostapd_interface_init()). One
example for such case is during WPS initialization when the code tries
to fetch the uuid from each of the interfaces.

Signed-off-by: Guy Eilam <guy@wizery.com>