tcp: add RETPOLINE mitigation to sk_backlog_rcv

mainline inclusion
from mainline-v5.17-rc1
commit d2489c7b
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I65HYE

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d2489c7b6d7d5ed4b32b56703c57c47bfbfe7fa5



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Use INDIRECT_CALL_INET() to avoid an indirect call
when/if CONFIG_RETPOLINE=y

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit d2489c7b)
Signed-off-by: Liu Jian <liujian56@huawei.com>