tcp: minor optimization in tcp_add_backlog()

stable inclusion
from stable-v5.10.153
commit 49713d7c38588311815889cb8c766591255ec836
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I64YCA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49713d7c38588311815889cb8c766591255ec836



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

[ Upstream commit d519f350 ]

If packet is going to be coalesced, sk_sndbuf/sk_rcvbuf values
are not used. Defer their access to the point we need them.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: ec791d81 ("tcp: fix a signed-integer-overflow bug in tcp_add_backlog()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Lipeng Sang <sanglipeng1@jd.com>