Documentation: convert nfsd-admin-interfaces to ReST

Convert nfsd-admin-interfaces to ReST and move it into admin-guide.
Content remains mostly untouched.

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Link: https://lore.kernel.org/r/d471305e9c96dec38f18d2ff816fca2269a88e29.1578697871.git.dwlsalmeida@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/nfs/index.rst

@@ -8,3 +8,4 @@ NFS
     nfs-client
     nfsroot
     nfs-rdma
+    nfsd-admin-interfaces

Documentation/admin-guide/nfs/nfsd-admin-interfaces.rst

@@ -1,5 +1,6 @@
+==================================
 Administrative interfaces for nfsd
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+==================================
 
 Note that normally these interfaces are used only by the utilities in
 nfs-utils.
@@ -13,18 +14,16 @@ nfsd/threads.
 Before doing that, NFSD can be told which sockets to listen on by
 writing to nfsd/portlist; that write may be:
 
-	- an ascii-encoded file descriptor, which should refer to a
-	  bound (and listening, for tcp) socket, or
-	- "transportname port", where transportname is currently either
-	  "udp", "tcp", or "rdma".
+	-  an ascii-encoded file descriptor, which should refer to a
+	   bound (and listening, for tcp) socket, or
+	-  "transportname port", where transportname is currently either
+	   "udp", "tcp", or "rdma".
 
 If nfsd is started without doing any of these, then it will create one
 udp and one tcp listener at port 2049 (see nfsd_init_socks).
 
-On startup, nfsd and lockd grace periods start.
-
-nfsd is shut down by a write of 0 to nfsd/threads.  All locks and state
-are thrown away at that point.
+On startup, nfsd and lockd grace periods start. nfsd is shut down by a write of
+0 to nfsd/threads.  All locks and state are thrown away at that point.
 
 Between startup and shutdown, the number of threads may be adjusted up
 or down by additional writes to nfsd/threads or by writes to
@@ -34,7 +33,7 @@ For more detail about files under nfsd/ and what they control, see
 fs/nfsd/nfsctl.c; most of them have detailed comments.
 
 Implementation notes
-^^^^^^^^^^^^^^^^^^^^
+====================
 
 Note that the rpc server requires the caller to serialize addition and
 removal of listening sockets, and startup and shutdown of the server.