MEDIUM: fd/poller: turn update_mask to group-local IDs

From now on, the FD's update_mask only refers to local thread IDs. However,
there remains a limitation, in updt_fd_polling(), we temporarily have to
check and set shared FDs against .thread_mask, which still contains global
ones. As such, nbtgroups > 1 may break (but this is not yet supported without
special build options).
diff --git a/src/stream.c b/src/stream.c
index 66529d4..4208885 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -3330,7 +3330,7 @@
 			              conn->flags,
 			              conn_fd(conn),
 			              conn_fd(conn) >= 0 ? fdtab[conn->handle.fd].state : 0,
-			              conn_fd(conn) >= 0 ? !!(fdtab[conn->handle.fd].update_mask & tid_bit) : 0,
+			              conn_fd(conn) >= 0 ? !!(fdtab[conn->handle.fd].update_mask & ti->ltid_bit) : 0,
 				      conn_fd(conn) >= 0 ? fdtab[conn->handle.fd].thread_mask: 0);
 
 		}
@@ -3368,7 +3368,7 @@
 			              conn->flags,
 			              conn_fd(conn),
 			              conn_fd(conn) >= 0 ? fdtab[conn->handle.fd].state : 0,
-			              conn_fd(conn) >= 0 ? !!(fdtab[conn->handle.fd].update_mask & tid_bit) : 0,
+			              conn_fd(conn) >= 0 ? !!(fdtab[conn->handle.fd].update_mask & ti->ltid_bit) : 0,
 				      conn_fd(conn) >= 0 ? fdtab[conn->handle.fd].thread_mask: 0);
 
 		}