Add editorconfig file.

EditorConfig is a file format and collection of text editor plugins for
maintaining consistent coding styles between different editors and IDEs.

Initialize the file following the coding rules in
Documentation/internals/contributing/coding-style.rst and add exceptions
declared in build-aux/initial-tab-allowed-files. Only enforce rules for
*.c and *.h files. Other files should use the default indenting rules
from text editors.

In order for this file to be taken into account (unless they use an
editor with built-in EditorConfig support), developers will have to
install a plugin.

Notes:

* All matching rules are considered. The last matching rule's properties
  will override the previous ones.
* The max_line_length property is only supported by a limited number of
  EditorConfig plugins. It will be ignored if unsupported.

Link: https://editorconfig.org/
Link: https://github.com/editorconfig/editorconfig-emacs
Link: https://github.com/editorconfig/editorconfig-vim
Link: https://github.com/editorconfig/editorconfig/wiki/EditorConfig-Properties#max_line_length
Signed-off-by: Robin Jarry <rjarry@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

.editorconfig

@@ -0,0 +1,48 @@
+# See https://editorconfig.org/ for syntax reference.
+
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+charset = utf-8
+
+[*.{c,h}]
+indent_style = space
+indent_size = 4
+max_line_length = 79
+
+[include/linux/**.h]
+indent_style = tab
+indent_size = tab
+tab_width = 8
+
+[include/sparse/rte_*.h]
+indent_style = tab
+tab_width = 8
+
+[include/windows/getopt.h]
+indent_style = tab
+indent_size = tab
+tab_width = 8
+
+[include/windows/netinet/{icmp6,ip6}.h]
+indent_style = tab
+indent_size = tab
+tab_width = 8
+
+[lib/getopt_long.c]
+indent_style = tab
+indent_size = tab
+tab_width = 8
+
+[lib/sflow*.{c,h}]
+indent_style = tab
+indent_size = tab
+tab_width = 8
+
+[lib/strsep.c]
+indent_style = tab
+indent_size = tab
+tab_width = 8

Makefile.am

@@ -82,6 +82,7 @@ EXTRA_DIST = \
 	.ci/osx-build.sh \
 	.ci/osx-prepare.sh \
 	.cirrus.yml \
+	.editorconfig \
 	.github/workflows/build-and-test.yml \
 	appveyor.yml \
 	boot.sh \