Clear the MAC Address field in device node

This avoids pushing garbage into the device node, e.g.:

00000000  07 00 00 00 01 00 00 00  44 00 54 00 45 00 53 00  |........D.T.E.S.|
00000010  54 00 32 00 00 00 03 0b  25 00 52 54 00 04 a7 a0  |T.2.....%.RT....|
00000020  00 00 00 00 00 00 00 00  65 66 69 76 61 72 73 2f  |........efivars/|
                                   ^^^^^^^^^^^^^^^^^^^^^^^
00000030  42 6f 6f 74 30 30 30 33  2d 38 01 03 0c 1b 00 00  |Boot0003-8......|
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
00000040  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000050  00 00 00 00 00 00 7f ff  04 00                    |..........|
0000005a

src/dp-message.c

@@ -628,6 +628,7 @@ efidp_make_mac_addr(uint8_t *buf, ssize_t size, uint8_t if_type,
 	ssize_t req = sizeof (*mac);
 	if (size && sz == req) {
 		mac->if_type = if_type;
+		memset(mac->mac_addr, 0, 32);
 		memcpy(mac->mac_addr, mac_addr,
 		       mac_addr_size > 32 ? 32 : mac_addr_size);
 	}