docs: networking: convert proc_net_tcp.txt to ReST

- add SPDX header;
- add a document title;
- mark code blocks and literals as such;
- mark tables 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

@@ -94,6 +94,7 @@ Contents:
    pktgen
    plip
    ppp_generic
+   proc_net_tcp
 
 .. only::  subproject and html
 

Documentation/networking/proc_net_tcp.txt → Documentation/networking/proc_net_tcp.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+============================================
+The proc/net/tcp and proc/net/tcp6 variables
+============================================
+
 This document describes the interfaces /proc/net/tcp and /proc/net/tcp6.
 Note that these interfaces are deprecated in favor of tcp_diag.
 
-These /proc interfaces provide information about currently active TCP 
+These /proc interfaces provide information about currently active TCP
 connections, and are implemented by tcp4_seq_show() in net/ipv4/tcp_ipv4.c
 and tcp6_seq_show() in net/ipv6/tcp_ipv6.c, respectively.
 
 It will first list all listening TCP sockets, and next list all established
-TCP connections. A typical entry of /proc/net/tcp would look like this (split 
-up into 3 parts because of the length of the line):
+TCP connections. A typical entry of /proc/net/tcp would look like this (split
+up into 3 parts because of the length of the line)::
 
-   46: 010310AC:9C4C 030310AC:1770 01 
+   46: 010310AC:9C4C 030310AC:1770 01
    |      |      |      |      |   |--> connection state
    |      |      |      |      |------> remote TCP port number
    |      |      |      |-------------> remote IPv4 address
@@ -17,7 +23,7 @@ up into 3 parts because of the length of the line):
    |      |---------------------------> local IPv4 address
    |----------------------------------> number of entry
 
-   00000150:00000000 01:00000019 00000000  
+   00000150:00000000 01:00000019 00000000
       |        |     |     |       |--> number of unrecovered RTO timeouts
       |        |     |     |----------> number of jiffies until timer expires
       |        |     |----------------> timer_active (see below)
@@ -25,7 +31,7 @@ up into 3 parts because of the length of the line):
       |-------------------------------> transmit-queue
 
    1000        0 54165785 4 cd1e6040 25 4 27 3 -1
-    |          |    |     |    |     |  | |  | |--> slow start size threshold, 
+    |          |    |     |    |     |  | |  | |--> slow start size threshold,
     |          |    |     |    |     |  | |  |      or -1 if the threshold
     |          |    |     |    |     |  | |  |      is >= 0xFFFF
     |          |    |     |    |     |  | |  |----> sending congestion window
@@ -40,9 +46,12 @@ up into 3 parts because of the length of the line):
     |---------------------------------------------> uid
 
 timer_active:
+
+ ==  ================================================================
   0  no timer is pending
   1  retransmit-timer is pending
   2  another timer (e.g. delayed ack or keepalive) is pending
-  3  this is a socket in TIME_WAIT state. Not all fields will contain 
+  3  this is a socket in TIME_WAIT state. Not all fields will contain
      data (or even exist)
   4  zero window probe timer is pending
+ ==  ================================================================