docs: networking: convert iphase.txt to ReST

- add SPDX header;
- adjust title using the proper markup;
- mark code blocks and literals as such;
- mark tables as such;
- mark lists as such;
- 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/index.rst

@@ -67,6 +67,7 @@ Contents:
    ila
    ipddp
    ip_dynaddr
+   iphase
 
 .. only::  subproject and html
 

drivers/atm/Kconfig

@@ -306,7 +306,7 @@ config ATM_IA
 	  for more info about the cards. Say Y (or M to compile as a module
 	  named iphase) here if you have one of these cards.
 
-	  See the file <file:Documentation/networking/iphase.txt> for further
+	  See the file <file:Documentation/networking/iphase.rst> for further
 	  details.
 
 config ATM_IA_DEBUG