net: introduce struct net_hotdata

Instead of spreading networking critical fields
all over the places, add a custom net_hotdata
structure so that we can precisely control its layout.

In this first patch, move :

- gro_normal_batch used in rx (GRO stack)
- offload_base used in rx and tx (GRO and TSO stacks)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240306160031.874438-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/hotdata.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _NET_HOTDATA_H
+#define _NET_HOTDATA_H
+
+#include <linux/types.h>
+
+/* Read mostly data used in network fast paths. */
+struct net_hotdata {
+	struct list_head	offload_base;
+	int			gro_normal_batch;
+};
+
+extern struct net_hotdata net_hotdata;
+
+#endif /* _NET_HOTDATA_H */