docs: networking: convert ipddp.txt to ReST

Not much to be done here:

- add SPDX header;
- use a document title from existing text;
- adjust a chapter markup;
- add to networking/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/index.rst

@@ -65,6 +65,7 @@ Contents:
    gtp
    hinic
    ila
+   ipddp
 
 .. only::  subproject and html
 

Documentation/networking/ipddp.txt → Documentation/networking/ipddp.rst

-Text file for ipddp.c:
-	AppleTalk-IP Decapsulation and AppleTalk-IP Encapsulation
+.. SPDX-License-Identifier: GPL-2.0
 
-This text file is written by Jay Schulist <jschlst@samba.org>
+=========================================================
+AppleTalk-IP Decapsulation and AppleTalk-IP Encapsulation
+=========================================================
+
+Documentation ipddp.c
+
+This file is written by Jay Schulist <jschlst@samba.org>
 
 Introduction
 ------------
@@ -21,7 +26,7 @@ kernel AppleTalk layer and drivers are available.
 Each mode requires its own user space software.
 
 Compiling AppleTalk-IP Decapsulation/Encapsulation
-=================================================
+==================================================
 
 AppleTalk-IP decapsulation needs to be compiled into your kernel. You
 will need to turn on AppleTalk-IP driver support. Then you will need to

Documentation/networking/ltpc.txt

@@ -99,7 +99,7 @@ treat the LocalTalk device like an ordinary Ethernet device, even if
 that's what it looks like to Netatalk.
 
 Instead, you follow the same procedure as for doing IP in EtherTalk.
-See Documentation/networking/ipddp.txt for more information about the
+See Documentation/networking/ipddp.rst for more information about the
 kernel driver and userspace tools needed.
 
 --------------------------------------

drivers/net/appletalk/Kconfig

@@ -86,7 +86,7 @@ config IPDDP
 	  box is stuck on an AppleTalk only network) or decapsulate (e.g. if
 	  you want your Linux box to act as an Internet gateway for a zoo of
 	  AppleTalk connected Macs). Please see the file
-	  <file:Documentation/networking/ipddp.txt> for more information.
+	  <file:Documentation/networking/ipddp.rst> for more information.
 
 	  If you say Y here, the AppleTalk-IP support will be compiled into
 	  the kernel. In this case, you can either use encapsulation or
@@ -107,4 +107,4 @@ config IPDDP_ENCAP
 	  IP packets inside AppleTalk frames; this is useful if your Linux box
 	  is stuck on an AppleTalk network (which hopefully contains a
 	  decapsulator somewhere). Please see
-	  <file:Documentation/networking/ipddp.txt> for more information.
+	  <file:Documentation/networking/ipddp.rst> for more information.