docs: networking: convert tuntap.txt to ReST

- add SPDX header;
- use copyright symbol;
- adjust titles and chapters, adding proper markups;
- mark code blocks and literals as such;
- adjust identation, whitespaces and blank lines where needed;
- 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

@@ -111,6 +111,7 @@ Contents:
    team
    timestamping
    tproxy
+   tuntap
 
 .. only::  subproject and html
 

MAINTAINERS

@@ -17161,7 +17161,7 @@ TUN/TAP driver
 M:	Maxim Krasnyansky <maxk@qti.qualcomm.com>
 S:	Maintained
 W:	http://vtun.sourceforge.net/tun
-F:	Documentation/networking/tuntap.txt
+F:	Documentation/networking/tuntap.rst
 F:	arch/um/os-Linux/drivers/
 
 TURBOCHANNEL SUBSYSTEM

drivers/net/Kconfig

@@ -355,7 +355,7 @@ config TUN
 	  devices, driver will automatically delete tunXX or tapXX device and
 	  all routes corresponding to it.
 
-	  Please read <file:Documentation/networking/tuntap.txt> for more
+	  Please read <file:Documentation/networking/tuntap.rst> for more
 	  information.
 
 	  To compile this driver as a module, choose M here: the module