fix wording

Author: vladak

network.tex

@@ -410,7 +410,7 @@
 to be used for web servers that distinguished virtual servers based on the IP
 address.  However, that is remote past.  To distinguish between virtual servers
 running on the same host, a HTTP header \uv{\texttt{Host:}} is used.  Similarly,
-the TLS protocol uses \texttt{ServerName}.
+the TLS protocol uses the \texttt{ServerName} extension.
 \item The fact that the system starts listening on a port means that a TCP
 handshake is performed and data is being accepted.  The data is stored
 in a fixed length buffer and after it is filled out, the connection is still