rust: net: netlink: Migrate to zerocopy's IntoBytes

Replace the kernel's own `transmute::FromBytes` and `AsBytes` traits
with their zerocopy equivalents. Specifically, this updates
`GenlMsg::put` to rely on `IntoBytes` for converting attributes into
byte slices.

Also, add `Immutable` trait bound on `GenlMsg::put` as zerocopy
splits the `no interior mutability` guarantee that `AsBytes` bundled
together.

Link: https://github.com/Rust-for-Linux/linux/issues/1241
Signed-off-by: Sagar Taunk <sagartaunk@proton.me>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260915144231.31932-1-sagartaunk@proton.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

rust/kernel/net/netlink.rs

@@ -12,7 +12,6 @@
     alloc::{self, AllocError},
     error::to_result,
     prelude::*,
-    transmute::AsBytes,
     types::Opaque,
     ThisModule,
 };
@@ -22,6 +21,11 @@
     ptr::NonNull, //
 };
 
+use zerocopy::{
+    Immutable,
+    IntoBytes, //
+};
+
 /// The default netlink message size.
 pub const GENLMSG_DEFAULT_SIZE: usize = bindings::GENLMSG_DEFAULT_SIZE;
 
@@ -84,7 +88,7 @@ impl GenlMsg {
     #[inline]
     fn put<T>(&mut self, attrtype: c_int, value: &T) -> Result
     where
-        T: ?Sized + AsBytes,
+        T: ?Sized + IntoBytes + Immutable,
     {
         let skb = self.skb.skb.as_ptr();
         let len = size_of_val(value);