checkpatch: Warn on code with 6+ tab indentation

Overly indented code should be refactored.

Suggest refactoring excessive indentation of of
if/else/for/do/while/switch statements.

For example:

$ cat t.c
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{

	if (1)
		if (2)
			if (3)
				if (4)
					if (5)
						if (6)
							if (7)
								if (8)
									;
	return 0;
}

$ ./scripts/checkpatch.pl -f t.c
WARNING: Too many leading tabs - consider code refactoring
#12: FILE: t.c:12:
+						if (6)

WARNING: Too many leading tabs - consider code refactoring
#13: FILE: t.c:13:
+							if (7)

WARNING: Too many leading tabs - consider code refactoring
#14: FILE: t.c:14:
+								if (8)

total: 0 errors, 3 warnings, 17 lines checked

t.c has style problems, please review.

If any of these errors are false positives, please report
them to the maintainer, see CHECKPATCH in MAINTAINERS.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -1924,6 +1924,12 @@ sub process {
 			my $pre_ctx = "$1$2";
 
 			my ($level, @ctx) = ctx_statement_level($linenr, $realcnt, 0);
+
+			if ($line =~ /^\+\t{6,}/) {
+				WARN("DEEP_INDENTATION",
+				     "Too many leading tabs - consider code refactoring\n" . $herecurr);
+			}
+
 			my $ctx_cnt = $realcnt - $#ctx - 1;
 			my $ctx = join("\n", @ctx);