[3691] Revised admin guide text based on review comments

doc/guide/dhcp6-srv.xml - revised text per review, removed extraneous whitespaces

doc/guide/dhcp6-srv.xml

@@ -2357,9 +2357,11 @@ should include options from the isc option space:
         that those addresses are based on EUI-64, which contains MAC address. This
         method is not completely reliable, as clients may use other link-local address
         types.  In particular, privacy extensions, defined in RFC4941, do not use
-        MAC addresses.  Also note that to extract successfully the address's u-bit must
-        be set to 1 and its g-bit must be set to 0 indicating that it is an interface
-        identifier per RFC 2373 section 2.5.1.
+        MAC addresses.  Also note that successful extraction requires that the
+        address's u-bit must be set to 1 and its g-bit set to 0, indicating that it
+        is an interface identifier as per
+        <ulink url="http://tools.ietf.org/html/rfc2373#section-2.5.1">
+        RFC 2373, section 2.5.1</ulink>.
         </simpara>
       </listitem>
       <listitem>