tcp: configurable source port perturb table size

stable inclusion
from stable-v5.10.157
commit 7e8eaa939eea93f961417e33f6d02db41e1f4fb6
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7MU59

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7e8eaa939eea93f961417e33f6d02db41e1f4fb6



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[ Upstream commit aeac4ec8 ]

On embedded systems with little memory and no relevant
security concerns, it is beneficial to reduce the size
of the table.

Reducing the size from 2^16 to 2^8 saves 255 KiB
of kernel RAM.

Makes the table size configurable as an expert option.

The size was previously increased from 2^8 to 2^16
in commit 4c2c8f03 ("tcp: increase source port perturb table to
2^16").

Signed-off-by: Gleb Mazovetskiy <glex.spb@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>