hostapd: Define CONFIG_SHA256 for SHA256 builds

wpa_supplicant was already doing this and hostapd will need to define
this for future additions.

Signed-hostap: Jouni Malinen <j@w1.fi>

hostapd/Makefile

@@ -678,6 +678,7 @@ endif
 endif
 
 ifdef NEED_SHA256
+CFLAGS += -DCONFIG_SHA256
 OBJS += ../src/crypto/sha256.o
 ifdef CONFIG_INTERNAL_SHA256
 OBJS += ../src/crypto/sha256-internal.o