tcpopt: remove KIND keyword

tcpopt: remove KIND keyword

tcp option <foo> kind ... never makes any sense, as "tcp option <foo>"
already tells the kernel to look for the foo <kind>.

"tcp option sack kind 5" matches if the sack option is present; its a
more complicated form of the simpler "tcp option sack exists".

"tcp option sack kind 1" (or any other value than 5) will never match.

So remove this.

Test cases are converted to "exists".

Signed-off-by: Florian Westphal <fw@strlen.de>