checkpatch: describe --min-conf-desc-length

Neither the warning nor the help message gives any hint on the unit for
length: Could be meters, inches, bytes, characters or ... lines.

Extend the output of `--help` to name the unit "lines" and the default:
- --min-conf-desc-length=n set the min description length, if shorter, warn
+ --min-conf-desc-length=n set the minimum description length for config symbols
+ in lines, if shorter, warn (default 4)

Include the minimum number of lines as other error messages already do:
- WARNING: please write a help paragraph that fully describes the config symbol
+ WARNING: please write a help paragraph that fully describes the config symbol with at least 4 lines

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Philipp Hahn <[e-mail]>
Cc: Andy Whitcroft <[e-mail]>
Cc: Joe Perches <[e-mail]>
Cc: Dwaipayan Ray <[e-mail]>
Cc: Lukas Bulwahn <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

scripts/checkpatch.pl

···
   --max-line-length=n        set the maximum line length, (default $max_line_length)
                              if exceeded, warn on patches
                              requires --strict for use with --file
-  --min-conf-desc-length=n   set the min description length, if shorter, warn
+  --min-conf-desc-length=n   set the minimum description length for config symbols
+                             in lines, if shorter, warn (default $min_conf_desc_length)
   --tab-size=n               set the number of spaces for tab (default $tabsize)
   --root=PATH                PATH to the kernel tree root
   --no-summary               suppress the per-file summary
···
 			    $help_length < $min_conf_desc_length) {
 				my $stat_real = get_stat_real($linenr, $ln - 1);
 				WARN("CONFIG_DESCRIPTION",
-				     "please write a help paragraph that fully describes the config symbol\n" . "$here\n$stat_real\n");
+				     "please write a help paragraph that fully describes the config symbol with at least $min_conf_desc_length lines\n" . "$here\n$stat_real\n");
 			}
 		}