Documentation: networking: ip-sysctl: drop doubled word

Drop the doubled word "that".
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.rst

@@ -741,7 +741,7 @@ tcp_fastopen - INTEGER
 
 	Default: 0x1
 
-	Note that that additional client or server features are only
+	Note that additional client or server features are only
 	effective if the basic support (0x1 and 0x2) are enabled respectively.
 
 tcp_fastopen_blackhole_timeout_sec - INTEGER