ftp: raise too_many_transactions event on overflow

Other parsers (SMB, POP3, ENIP) already raise a too_many_transactions
event when a flow exceeds its per-flow transaction limit. FTP had
the limit wired up through app-layer.protocols.ftp.max-tx but just
dropped the excess transaction on the floor with a "FTP does not set
events yet..." TODO, so no event was raised when the limit was
reached.

Add the FtpEventTooManyTransactions variant, a stock rule at
sid 2232002, and raise the event from FTPTransactionCreate when the
live-tx count goes past ftp_config_maxtx.

Issue: 8489

rust/src/ftp/event.rs

@@ -25,6 +25,8 @@ pub enum FtpEvent {
     FtpEventRequestCommandTooLong,
     #[name("response_command_too_long")]
     FtpEventResponseCommandTooLong,
+    #[name("too_many_transactions")]
+    FtpEventTooManyTransactions,
 }
 
 /// Wrapper around the Rust generic function for get_event_info.

src/app-layer-ftp.c

@@ -223,7 +223,10 @@ static FTPTransaction *FTPTransactionCreate(FtpState *state)
     SCEnter();
     FTPTransaction *firsttx = TAILQ_FIRST(&state->tx_list);
     if (firsttx && state->tx_cnt - firsttx->tx_id > ftp_config_maxtx) {
-        // FTP does not set events yet...
+        FTPTransaction *event_tx = state->curr_tx ? state->curr_tx : firsttx;
+        event_tx->done = true;
+        event_tx->tx_data.updated_ts = true;
+        SCAppLayerDecoderEventsSetEventRaw(&event_tx->tx_data.events, FtpEventTooManyTransactions);
         return NULL;
     }
     FTPTransaction *tx = FTPCalloc(1, sizeof(*tx));