Fix some markup errors.

Doc/lib/libsocket.tex

@@ -19,8 +19,8 @@ for the various socket-related system calls are also a valuable source
 of information on the details of socket semantics.  For \UNIX, refer
 to the manual pages; for Windows, see the WinSock (or Winsock 2)
 specification.
-For IPv6-ready APIs, readers may want to refer to RFC2553 titled
-\cite{Basic Socket Interface Extensions for IPv6}.
+For IPv6-ready APIs, readers may want to refer to \rfc{2553} titled
+\citetitle{Basic Socket Interface Extensions for IPv6}.
 
 The Python interface is a straightforward transliteration of the
 \UNIX{} system call and library interface for sockets to Python's