rust: phy: implement Send for Registration

In preparation for requiring `Send` for `Module` implementations in the
next patch.

Cc: FUJITA Tomonori <[email protected]>
Cc: Trevor Gross <[email protected]>
Cc: [email protected]
Signed-off-by: Wedson Almeida Filho <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Miguel Ojeda <[email protected]>

rust/kernel/net/phy.rs

@@ -640,6 +640,10 @@ pub struct Registration {
     drivers: Pin<&'static mut [DriverVTable]>,
 }
 
+// SAFETY: The only action allowed in a `Registration` instance is dropping it, which is safe to do
+// from any thread because `phy_drivers_unregister` can be called from any thread context.
+unsafe impl Send for Registration {}
+
 impl Registration {
     /// Registers a PHY driver.
     pub fn register(