Don't recommend the -r flag to mountd.

It enables a non-standards compliant feature to support ancient
diskless terminals.  We shouldn't recommend it without explanation.
(-r is currently the default in /etc/defaults/rc.conf along with -S,
this should likely be revisited.)

Instead, suggest setting mountd_enable.  While not required to start
the NFS server, it is required for the "service mountd restart" command
below.

Reviewed by:	bcr
Differential Revision:	https://reviews.freebsd.org/D25760

en_US.ISO8859-1/books/handbook/network-servers/chapter.xml

@@ -715,7 +715,7 @@ server-program-arguments</programlisting>
 
       <programlisting>rpcbind_enable="YES"
 nfs_server_enable="YES"
-mountd_flags="-r"</programlisting>
+mountd_enable="YES"</programlisting>
 
       <para>The server can be started now by running this
 	command:</para>