NFC: digital: Ensure no NAD byte in DEP_REQ and DEP_RES frames

According to chapter 14 of the NFC-DEP Digital
Protocol Spec., the NAD byte should never be
present in DEP_REQ or DEP_RES frames.  However,
this is not enforced so add that enforcement code.
Reviewed-by: Thierry Escande <thierry.escande@linux.intel.com>
Tested-by: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

net/nfc/digital_dep.c

@@ -420,6 +420,11 @@ static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg,
 		goto error;
 	}
 
+	if (DIGITAL_NFC_DEP_NAD_BIT_SET(pfb)) {
+		rc = -EIO;
+		goto exit;
+	}
+
 	if (size > resp->len) {
 		rc = -EIO;
 		goto error;
@@ -572,6 +577,11 @@ static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
 		goto exit;
 	}
 
+	if (DIGITAL_NFC_DEP_NAD_BIT_SET(pfb)) {
+		rc = -EIO;
+		goto exit;
+	}
+
 	if (size > resp->len) {
 		rc = -EIO;
 		goto exit;