rdp: fix tx id handling

Tx ID handling did not take the required + 1 into account.

From a report:

        RDP can skip cleanup because its id convention does not match the
        generic Rust iterator. The generic iterator in applayer.rs returns
        tx.id() - 1, and cleanup trusts that id when calling StateTransactionFree
        in app-layer-parser.c. RDP registers that iterator in rdp.rs, but
        RdpTransaction::id() returns the stored id unchanged in rdp.rs, while
        free_tx also compares against the raw stored id in rdp.rs. For a single
        freeable RDP tx with stored id 1, the iterator returns C id 0; cleanup
        calls free_tx(0), nothing is removed, then has_next == false allows
        min_id to advance to total_txs in app-layer-parser.c. That leaves the
        tx live but now below min_id, so later cleanup will not revisit it.

This patch brings the handling in line with the other parsers.

Bug: #8717.

rust/src/rdp/rdp.rs

@@ -146,7 +146,7 @@ impl RdpState {
         let mut index = 0;
         for ii in 0..len {
             let tx = &self.transactions[ii];
-            if tx.id == tx_id {
+            if tx.id == tx_id + 1 {
                 found = true;
                 index = ii;
                 break;
@@ -158,7 +158,7 @@ impl RdpState {
     }
 
     fn get_tx(&self, tx_id: u64) -> Option<&RdpTransaction> {
-        self.transactions.iter().find(|&tx| tx.id == tx_id)
+        self.transactions.iter().find(|&tx| tx.id == tx_id + 1)
     }
 
     fn new_tx(&mut self, item: RdpTransactionItem, direction: Direction) -> RdpTransaction {
@@ -721,7 +721,7 @@ mod tests {
         state.transactions.push_back(tx0);
         state.transactions.push_back(tx1);
         state.transactions.push_back(tx2);
-        assert_eq!(Some(&state.transactions[1]), state.get_tx(2));
+        assert_eq!(Some(&state.transactions[1]), state.get_tx(1));
     }
 
     #[test]
@@ -742,11 +742,11 @@ mod tests {
         state.transactions.push_back(tx0);
         state.transactions.push_back(tx1);
         state.transactions.push_back(tx2);
-        state.free_tx(1);
+        state.free_tx(0);
         assert_eq!(3, state.next_id);
         assert_eq!(2, state.transactions.len());
         assert_eq!(2, state.transactions[0].id);
         assert_eq!(3, state.transactions[1].id);
-        assert_eq!(None, state.get_tx(1));
+        assert_eq!(None, state.get_tx(0));
     }
 }