wpa_supplicant: Fix couple of C++ compiler errors with header files

Need to include these headers in C++ files for adding a binder interface
to wpa_supplicant. So, fix the following C++ compiler errors in them:
1. Add explicit C-style casts in wpa_buf.h header.
2. Move the nested definition of wpa_driver_scan_ssid in driver.h
outside of wpa_driver_scan_params because it is used in another
structure below.

Signed-off-by: Roshan Pius <rpius@google.com>

src/drivers/driver.h

@@ -292,6 +292,18 @@ struct wpa_interface_info {
 
 #define WPAS_MAX_SCAN_SSIDS 16
 
+/**
+ * struct wpa_driver_scan_ssid - SSIDs to scan for
+ * @ssid - specific SSID to scan for (ProbeReq)
+ *	%NULL or zero-length SSID is used to indicate active scan
+ *	with wildcard SSID.
+ * @ssid_len - Length of the SSID in octets
+ */
+struct wpa_driver_scan_ssid {
+	const u8 *ssid;
+	size_t ssid_len;
+};
+
 /**
  * struct wpa_driver_scan_params - Scan parameters
  * Data for struct wpa_driver_ops::scan2().
@@ -300,18 +312,7 @@ struct wpa_driver_scan_params {
 	/**
 	 * ssids - SSIDs to scan for
 	 */
-	struct wpa_driver_scan_ssid {
-		/**
-		 * ssid - specific SSID to scan for (ProbeReq)
-		 * %NULL or zero-length SSID is used to indicate active scan
-		 * with wildcard SSID.
-		 */
-		const u8 *ssid;
-		/**
-		 * ssid_len: Length of the SSID in octets
-		 */
-		size_t ssid_len;
-	} ssids[WPAS_MAX_SCAN_SSIDS];
+	struct wpa_driver_scan_ssid ssids[WPAS_MAX_SCAN_SSIDS];
 
 	/**
 	 * num_ssids - Number of entries in ssids array

src/utils/wpabuf.h

@@ -81,7 +81,7 @@ static inline const void * wpabuf_head(const struct wpabuf *buf)
 
 static inline const u8 * wpabuf_head_u8(const struct wpabuf *buf)
 {
-	return wpabuf_head(buf);
+	return (const u8 *) wpabuf_head(buf);
 }
 
 /**
@@ -96,42 +96,42 @@ static inline void * wpabuf_mhead(struct wpabuf *buf)
 
 static inline u8 * wpabuf_mhead_u8(struct wpabuf *buf)
 {
-	return wpabuf_mhead(buf);
+	return (u8 *) wpabuf_mhead(buf);
 }
 
 static inline void wpabuf_put_u8(struct wpabuf *buf, u8 data)
 {
-	u8 *pos = wpabuf_put(buf, 1);
+	u8 *pos = (u8 *) wpabuf_put(buf, 1);
 	*pos = data;
 }
 
 static inline void wpabuf_put_le16(struct wpabuf *buf, u16 data)
 {
-	u8 *pos = wpabuf_put(buf, 2);
+	u8 *pos = (u8 *) wpabuf_put(buf, 2);
 	WPA_PUT_LE16(pos, data);
 }
 
 static inline void wpabuf_put_le32(struct wpabuf *buf, u32 data)
 {
-	u8 *pos = wpabuf_put(buf, 4);
+	u8 *pos = (u8 *) wpabuf_put(buf, 4);
 	WPA_PUT_LE32(pos, data);
 }
 
 static inline void wpabuf_put_be16(struct wpabuf *buf, u16 data)
 {
-	u8 *pos = wpabuf_put(buf, 2);
+	u8 *pos = (u8 *) wpabuf_put(buf, 2);
 	WPA_PUT_BE16(pos, data);
 }
 
 static inline void wpabuf_put_be24(struct wpabuf *buf, u32 data)
 {
-	u8 *pos = wpabuf_put(buf, 3);
+	u8 *pos = (u8 *) wpabuf_put(buf, 3);
 	WPA_PUT_BE24(pos, data);
 }
 
 static inline void wpabuf_put_be32(struct wpabuf *buf, u32 data)
 {
-	u8 *pos = wpabuf_put(buf, 4);
+	u8 *pos = (u8 *) wpabuf_put(buf, 4);
 	WPA_PUT_BE32(pos, data);
 }