dcerpc/tcp: fix compile warning

warning: variable does not need to be mutable
    --> src/dcerpc/dcerpc.rs:1036:42
     |
1036 |                     let tx = if let Some(mut tx) = self.get_tx_by_call_id(current_call_id, core::STREAM_TOCLIENT) {
     |                                          ----^^
     |                                          |
     |                                          help: remove this `mut`
     |
     = note: `#[warn(unused_mut)]` on by default

warning: variable does not need to be mutable
    --> src/dcerpc/dcerpc.rs:1061:30
     |
1061 |                         Some(mut tx) => {
     |                              ----^^
     |                              |
     |                              help: remove this `mut`

rust/src/dcerpc/dcerpc.rs

@@ -1033,7 +1033,7 @@ impl DCERPCState {
                     if retval == -1 {
                         return AppLayerResult::err();
                     }
-                    let tx = if let Some(mut tx) = self.get_tx_by_call_id(current_call_id, core::STREAM_TOCLIENT) {
+                    let tx = if let Some(tx) = self.get_tx_by_call_id(current_call_id, core::STREAM_TOCLIENT) {
                         tx.resp_cmd = x;
                         tx
                     } else {
@@ -1058,7 +1058,7 @@ impl DCERPCState {
                 DCERPC_TYPE_RESPONSE => {
                     let transaction = self.get_tx_by_call_id(current_call_id, core::STREAM_TOCLIENT);
                     match transaction {
-                        Some(mut tx) => {
+                        Some(tx) => {
                             tx.resp_cmd = x;
                         }
                         None => {