move trans->assignment_done to cc.assignment_started

The flag is set to true when an assignment has been started, and it is only
relevant for a CC transaction. So fix naming and place in cc struct.

Cosmetic preparation for I1f8746e7babfcd3028a4d2c0ba260c608c686c76 and
I0ba216b737909e92080a722db26e3577726c63cb/

Change-Id: I8dacf46141ba0b664e85b0867ade330c97d8495f
diff --git a/src/libmsc/msc_mgcp.c b/src/libmsc/msc_mgcp.c
index 5a8ee79..8e2e7a9 100644
--- a/src/libmsc/msc_mgcp.c
+++ b/src/libmsc/msc_mgcp.c
@@ -951,7 +951,7 @@
 	.event_names = msc_mgcp_fsm_evt_names,
 };
 
-/* Try to invoke call assignment and set trans->assignment_done flag if invoked.
+/* Try to invoke call assignment and set trans->cc.assignment_started flag if invoked.
  * This is relevant for already ongoing calls -- scenario:
  *  - subscriber is in an active voice call,
  *  - another call is coming in.
@@ -960,10 +960,10 @@
 int msc_mgcp_try_call_assignment(struct gsm_trans *trans)
 {
 	struct ran_conn *conn = trans->conn;
-	if (trans->assignment_done)
+	if (trans->cc.assignment_started)
 		return 0;
 	LOGPFSMSL(conn->fi, DMGCP, LOGL_INFO, "Starting call assignment\n");
-	trans->assignment_done = true;
+	trans->cc.assignment_started = true;
 	return msc_mgcp_call_assignment(trans);
 }