docs: networking: convert filter.txt to ReST

- add SPDX header;
- adjust title markup;
- mark code blocks and literals as such;
- use footnote markup;
- mark tables 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/bpf/index.rst

@@ -7,7 +7,7 @@ Filter) facility, with a focus on the extended BPF version (eBPF).
 
 This kernel side documentation is still work in progress.  The main
 textual documentation is (for historical reasons) described in
-`Documentation/networking/filter.txt`_, which describe both classical
+`Documentation/networking/filter.rst`_, which describe both classical
 and extended BPF instruction-set.
 The Cilium project also maintains a `BPF and XDP Reference Guide`_
 that goes into great technical depth about the BPF Architecture.
@@ -59,7 +59,7 @@ Testing and debugging BPF
 
 
 .. Links:
-.. _Documentation/networking/filter.txt: ../networking/filter.txt
+.. _Documentation/networking/filter.rst: ../networking/filter.txt
 .. _man-pages: https://www.kernel.org/doc/man-pages/
 .. _bpf(2): http://man7.org/linux/man-pages/man2/bpf.2.html
 .. _BPF and XDP Reference Guide: http://cilium.readthedocs.io/en/latest/bpf/

Documentation/networking/index.rst

@@ -56,6 +56,7 @@ Contents:
    driver
    eql
    fib_trie
+   filter
 
 .. only::  subproject and html
 

Documentation/networking/packet_mmap.txt

@@ -1051,7 +1051,7 @@ for more information on hardware timestamps.
 -------------------------------------------------------------------------------
 
 - Packet sockets work well together with Linux socket filters, thus you also
-  might want to have a look at Documentation/networking/filter.txt
+  might want to have a look at Documentation/networking/filter.rst
 
 --------------------------------------------------------------------------------
 + THANKS

MAINTAINERS

@@ -3192,7 +3192,7 @@ Q:	https://patchwork.ozlabs.org/project/netdev/list/?delegate=77147
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
 F:	Documentation/bpf/
-F:	Documentation/networking/filter.txt
+F:	Documentation/networking/filter.rst
 F:	arch/*/net/*
 F:	include/linux/bpf*
 F:	include/linux/filter.h

tools/bpf/bpf_asm.c

@@ -11,7 +11,7 @@
  *
  * How to get into it:
  *
- * 1) read Documentation/networking/filter.txt
+ * 1) read Documentation/networking/filter.rst
  * 2) Run `bpf_asm [-c] <filter-prog file>` to translate into binary
  *    blob that is loadable with xt_bpf, cls_bpf et al. Note: -c will
  *    pretty print a C-like construct.

tools/bpf/bpf_dbg.c

@@ -13,7 +13,7 @@
  * for making a verdict when multiple simple BPF programs are combined
  * into one in order to prevent parsing same headers multiple times.
  *
- * More on how to debug BPF opcodes see Documentation/networking/filter.txt
+ * More on how to debug BPF opcodes see Documentation/networking/filter.rst
  * which is the main document on BPF. Mini howto for getting started:
  *
  *  1) `./bpf_dbg` to enter the shell (shell cmds denoted with '>'):