docs: networking: convert framerelay.txt to ReST

- add SPDX header;
- add a document title;
- adjust identation, whitespaces and blank lines;
- 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/framerelay.txt → Documentation/networking/framerelay.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+================
+Frame Relay (FR)
+================
+
 Frame Relay (FR) support for linux is built into a two tiered system of device
 drivers.  The upper layer implements RFC1490 FR specification, and uses the
 Data Link Connection Identifier (DLCI) as its hardware address.  Usually these
@@ -36,4 +42,3 @@ the net-tools distribution.  They can be found at ftp.invlogic.com, in
 /pub/linux.  Note that with OS/2 FTPD, you end up in /pub by default, so just
 use 'cd linux'.  v0.10 is for use on pre-2.0.3 and earlier, v0.15 is for
 pre-2.0.4 and later.
-

Documentation/networking/index.rst

@@ -58,6 +58,7 @@ Contents:
    fib_trie
    filter
    fore200e
+   framerelay
 
 .. only::  subproject and html
 

drivers/net/wan/Kconfig

@@ -336,7 +336,7 @@ config DLCI
 
 	  To use frame relay, you need supporting hardware (called FRAD) and
 	  certain programs from the net-tools package as explained in
-	  <file:Documentation/networking/framerelay.txt>.
+	  <file:Documentation/networking/framerelay.rst>.
 
 	  To compile this driver as a module, choose M here: the
 	  module will be called dlci.
@@ -361,7 +361,7 @@ config SDLA
 
 	  These are multi-protocol cards, but only Frame Relay is supported
 	  by the driver at this time. Please read
-	  <file:Documentation/networking/framerelay.txt>.
+	  <file:Documentation/networking/framerelay.rst>.
 
 	  To compile this driver as a module, choose M here: the
 	  module will be called sdla.