gsm0408_clear_request(): actually free the released conn

By having conn->in_release == 1, calling msc_release_connection() has no
effect and thus never frees the conn. So, after all pending requests have
been discarded, also discard and free the unused connection.

openbsc/src/libmsc/gsm_04_08.c

@@ -453,6 +453,8 @@ restart:
 			goto restart;
 		}
 	}
+
+	msc_subscr_con_free(conn);
 }
 
 void gsm0408_clear_all_trans(struct gsm_network *net, int protocol)