docs: networking: convert radiotap-headers.txt to ReST

- add SPDX header;
- adjust title markup;
- 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

@@ -95,6 +95,7 @@ Contents:
    plip
    ppp_generic
    proc_net_tcp
+   radiotap-headers
 
 .. only::  subproject and html
 

Documentation/networking/mac80211-injection.rst

@@ -13,7 +13,7 @@ following format::
  [ payload ]
 
 The radiotap format is discussed in
-./Documentation/networking/radiotap-headers.txt.
+./Documentation/networking/radiotap-headers.rst.
 
 Despite many radiotap parameters being currently defined, most only make sense
 to appear on received packets.  The following information is parsed from the

Documentation/networking/radiotap-headers.rst

@@ -1,3 +1,6 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========================
 How to use radiotap headers
 ===========================
 
@@ -5,7 +8,7 @@ Pointer to the radiotap include file
 ------------------------------------
 
 Radiotap headers are variable-length and extensible, you can get most of the
-information you need to know on them from:
+information you need to know on them from::
 
     ./include/net/ieee80211_radiotap.h
 
@@ -21,6 +24,8 @@ of the it_present member of ieee80211_radiotap_header is set, it means that
 the header for argument index 0 (IEEE80211_RADIOTAP_TSFT) is present in the
 argument area.
 
+::
+
    < 8-byte ieee80211_radiotap_header >
    [ <possible argument bitmap extensions ... > ]
    [ <argument> ... ]
@@ -76,6 +81,8 @@ ieee80211_radiotap_header.
 Example valid radiotap header
 -----------------------------
 
+::
+
 	0x00, 0x00, // <-- radiotap version + pad byte
 	0x0b, 0x00, // <- radiotap header length
 	0x04, 0x0c, 0x00, 0x00, // <-- bitmap
@@ -89,7 +96,7 @@ Using the Radiotap Parser
 
 If you are having to parse a radiotap struct, you can radically simplify the
 job by using the radiotap parser that lives in net/wireless/radiotap.c and has
-its prototypes available in include/net/cfg80211.h.  You use it like this:
+its prototypes available in include/net/cfg80211.h.  You use it like this::
 
     #include <net/cfg80211.h>
 

include/net/cfg80211.h

@@ -5211,7 +5211,7 @@ u32 ieee80211_mandatory_rates(struct ieee80211_supported_band *sband,
  * Radiotap parsing functions -- for controlled injection support
  *
  * Implemented in net/wireless/radiotap.c
- * Documentation in Documentation/networking/radiotap-headers.txt
+ * Documentation in Documentation/networking/radiotap-headers.rst
  */
 
 struct radiotap_align_size {

net/wireless/radiotap.c

@@ -90,7 +90,7 @@ static const struct ieee80211_radiotap_namespace radiotap_ns = {
  * iterator.this_arg for type "type" safely on all arches.
  *
  * Example code:
- * See Documentation/networking/radiotap-headers.txt
+ * See Documentation/networking/radiotap-headers.rst
  */
 
 int ieee80211_radiotap_iterator_init(