Trigger PACCH assignment inside dl_tbf_upgrade_to_multislot()

The triggering of the assignment for the new TBF allocation is part of
the "upgrade to multislot" process, hence move that inside the function.

Change-Id: Ic2b959f2476b900cb263ccd8f6698ed843bafd29
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index c5ce666..16dc47b 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -467,6 +467,8 @@
 		tbf->set_window_size();
 	tbf_update_state_fsm_name(tbf);
 
+	/* Now trigger the assignment using the pre-existing TBF: */
+	dl_tbf_trigger_ass_on_pacch(tbf, dl_tbf_as_tbf(tbf));
 	return 0;
 }