When timestamp support has been negotiated, TCP segements received without a timestamp should be discarded. However, there are broken TCP implementations (for example, stacks used by Omniswitch 63xx and 64xx models), which send TCP segments without timestamps although
they negotiated timestamp support.
This patch adds a sysctl variable which tolerates such TCP segments and allows to interoperate with broken stacks.

The issue was reported in PR 252449