Revert "tcp: avoid atomic operations on sk->sk_rmem_alloc"

Revert "tcp: avoid atomic operations on sk->sk_rmem_alloc"

This reverts commit 0de2a5c4b824da2205658ebebb99a55c43cdf60f.

I forgot that a TCP socket could receive messages in its error queue.

sock_queue_err_skb() can be called without socket lock being held,
and changes sk->sk_rmem_alloc.

The fact that skbs in error queue are limited by sk->sk_rcvbuf
means that error messages can be dropped if socket receive
queues are full, which is an orthogonal issue.

In future kernels, we could use a separate sk->sk_error_mem_alloc
counter specifically for the error queue.

Fixes: 0de2a5c4b824 ("tcp: avoid atomic operations on sk->sk_rmem_alloc")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250331075946.31960-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>