Make Ext a trait

kernel/libs/aster-bigtcp/src/ext.rs

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use crate::iface::ScheduleNextPoll;
+
+/// Extension to be implemented by users of this crate.
+///
+/// This should be implemented on an empty type that carries no data, since the type will never
+/// actually be instantiated.
+///
+/// The purpose of having this trait is to allow users of this crate to inject multiple types
+/// without the hassle of writing multiple trait bounds, which can be achieved by using the types
+/// associated with this trait.
+pub trait Ext {
+    /// The type for ifaces to schedule the next poll.
+    type ScheduleNextPoll: ScheduleNextPoll;
+}