nfs: explicity free files

In preparation of adding an argument to the free functions which
means the drop trait can't be used anymore.

rust/src/nfs/nfs.rs

@@ -258,6 +258,10 @@ impl Transaction for NFSTransaction {
 
 impl Drop for NFSTransaction {
     fn drop(&mut self) {
+        if let Some(NFSTransactionTypeData::FILE(ref mut tdf)) = self.type_data {
+            tdf.files.files_ts.free();
+            tdf.files.files_tc.free();
+        }
         self.free();
     }
 }