inet: frags: annotate races around fqdir->dead and fqdir->high_thresh

stable inclusion
from stable-v5.10.94
commit edc09548ffc52433ed25ef4a829e664e353f615d
bugzilla: https://gitee.com/openeuler/kernel/issues/I531X9

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=edc09548ffc52433ed25ef4a829e664e353f615d



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

commit 91341fa0 upstream.

Both fields can be read/written without synchronization,
add proper accessors and documentation.

Fixes: d5dd8879 ("inet: fix various use-after-free in defrags units")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>