nfc: st21nfca: Add additional comments about EVT_TRANSACTION

Add comments about HCI EVT_TRANSACTION in order to make the code
understandable by other readers.

Signed-off-by: Christophe Ricard <[e-mail]>
Signed-off-by: Samuel Ortiz <[e-mail]>

drivers/nfc/st21nfca/st21nfca_se.c

···
 	case ST21NFCA_EVT_CONNECTIVITY:
 		break;
 	case ST21NFCA_EVT_TRANSACTION:
+		/*
+		 * According to specification etsi 102 622
+		 * 11.2.2.4 EVT_TRANSACTION Table 52
+		 * Description	Tag	Length
+		 * AID		81	5 to 16
+		 * PARAMETERS	82	0 to 255
+		 */
 		if (skb->len < NFC_MIN_AID_LENGTH + 2 &&
 		    skb->data[0] != NFC_EVT_TRANSACTION_AID_TAG)
 			return -EPROTO;
···
 						   skb->len - 2, GFP_KERNEL);
 
 		transaction->aid_len = skb->data[1];
-		memcpy(transaction->aid, &skb->data[2], skb->data[1]);
+		memcpy(transaction->aid, &skb->data[2],
+		       transaction->aid_len);
 
+		/* Check next byte is PARAMETERS tag (82) */
 		if (skb->data[transaction->aid_len + 2] !=
 		    NFC_EVT_TRANSACTION_PARAMS_TAG)
 			return -EPROTO;