tcp: refactor tcp_retransmit_timer()

stable inclusion
from stable-v4.19.318
commit e5a1f7427f97bde4bda73c02106c3bde87696f8f
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAD4B4
CVE: CVE-2024-41007

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e5a1f7427f97bde4bda73c02106c3bde87696f8f



---------------------------

commit 0d580fbd upstream.

It appears linux-4.14 stable needs a backport of commit
88f8598d ("tcp: exit if nothing to retransmit on RTO timeout")

Since tcp_rtx_queue_empty() is not in pre 4.15 kernels,
let's refactor tcp_retransmit_timer() to only use tcp_rtx_queue_head()

I will provide to stable teams the squashed patches.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>