patch 9.1.1173: filetype: ABNF files are not detected

Problem:  filetype: ABNF files are not detected
Solution: detect '.abnf' file as abnf filetype and
          include an abnf syntax plugin (A4-Tacks).

References:
- RFC5234
- RFC7405

closes: #16802

Signed-off-by: A4-Tacks <wdsjxhno1001@163.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1173,
 /**/
     1172,
 /**/