Documentation/tcp: Fix an obvious typo

Yep, my VIM spellchecker is not good enough for typos like this one.

Fixes: 7fe0e38bb669 ("Documentation/tcp: Add TCP-AO documentation")
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Reported-by: Markus Elfring <Markus.Elfring@web.de>
Closes: https://lore.kernel.org/all/2745ab4e-acac-40d4-83bf-37f2600d0c3d@web.de/
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Documentation/tcp: Add TCP-AO documentation

It has Frequently Asked Questions (FAQ) on RFC 5925 - I found it very
useful answering those before writing the actual code. It provides answers
to common questions that arise on a quick read of the RFC, as well as how
they were answered. There's also comparison to TCP-MD5 option,
evaluation of per-socket vs in-kernel-DB approaches and description of
uAPI provided.

Hopefully, it will be as useful for reviewing the code as it was for writing.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Dmitry Safonov <dima@arista.com>
Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>