[PATCH v2] rust: net: netlink: Migrate to zerocopy's IntoBytes

[Sagar Taunk <sagartaunk@proton.me>]

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>
---
v2: Split into a separate patch per Shashiko's review; validates the
    attribute length with c_int::try_from() instead of casting with `as`.

 rust/kernel/net/netlink.rs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/net/netlink.rs b/rust/kernel/net/netlink.rs
index 22ef3dde36fa..3c2b142a7402 100644
--- a/rust/kernel/net/netlink.rs
+++ b/rust/kernel/net/netlink.rs
@@ -12,11 +12,12 @@
     alloc::{self, AllocError},
     error::to_result,
     prelude::*,
-    transmute::AsBytes,
     types::Opaque,
     ThisModule,
 };
 
+use zerocopy::{Immutable, IntoBytes};
+
 use core::{
     mem::ManuallyDrop,
     ptr::NonNull, //
@@ -84,7 +85,7 @@ 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);
-- 
2.55.0