nfs: add debug validation on file counts

(cherry picked from commit 1b3c3225cd)

rust/src/nfs/nfs.rs

@@ -215,6 +215,8 @@ impl NFSTransaction {
     }
 
     pub fn free(&mut self) {
+        debug_validate_bug_on!(self.tx_data.files_opened > 1);
+        debug_validate_bug_on!(self.tx_data.files_logged > 1);
         if self.events != std::ptr::null_mut() {
             sc_app_layer_decoder_events_free_events(&mut self.events);
         }