Revert "net: group sk_backlog and sk_receive_queue"

This reverts commit 4effb33.

This was a benefit for UDP flood case, which was later greatly improved
with commits 6471658 ("udp: use skb_attempt_defer_free()")
and b650bf0 ("udp: remove busylock and add per NUMA queues").

Apparently blamed commit added a regression for RAW sockets, possibly
because they do not use the dual RX queue strategy that UDP has.

sock_queue_rcv_skb_reason() and RAW recvmsg() compete for sk_receive_buf
and sk_rmem_alloc changes, and them being in the same
cache line reduce performance.

Fixes: 4effb33 ("net: group sk_backlog and sk_receive_queue")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202509281326.f605b4eb-lkp@intel.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: David Ahern <dsahern@kernel.org>
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250929182112.824154-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

include/net/sock.h

@@ -395,6 +395,7 @@ struct sock {
 
 	atomic_t		sk_drops;
 	__s32			sk_peek_off;
+	struct sk_buff_head	sk_error_queue;
 	struct sk_buff_head	sk_receive_queue;
 	/*
 	 * The backlog queue is special, it is always used with
@@ -412,7 +413,6 @@ struct sock {
 	} sk_backlog;
 #define sk_rmem_alloc sk_backlog.rmem_alloc
 
-	struct sk_buff_head	sk_error_queue;
 	__cacheline_group_end(sock_write_rx);
 
 	__cacheline_group_begin(sock_read_rx);