UBIFS: introduce helper functions for debugging checks and tests

This patch introduces helper functions for all debugging checks, so instead of
doing

if (!(ubifs_chk_flags & UBIFS_CHK_GEN))

we now do

if (!dbg_is_chk_gen(c))

This is a preparation to further changes where the flags will go away, and
we'll need to only change the helper functions, but the code which utilizes
them won't be touched.

At the same time this patch removes 'dbg_force_in_the_gaps()',
'dbg_force_in_the_gaps_enabled()', and dbg_failure_mode helpers for
consistency.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/tnc_commit.c b/fs/ubifs/tnc_commit.c
index d6fab1a..8959c72 100644
--- a/fs/ubifs/tnc_commit.c
+++ b/fs/ubifs/tnc_commit.c
@@ -23,6 +23,7 @@
 /* This file implements TNC functions for committing */
 
 #include "ubifs.h"
+#include <linux/random.h>
 
 /**
  * make_idx_node - make an index node for fill-the-gaps method of TNC commit.
@@ -381,7 +382,7 @@
 				c->gap_lebs = NULL;
 				return err;
 			}
-			if (dbg_force_in_the_gaps_enabled()) {
+			if (!dbg_is_chk_gen(c)) {
 				/*
 				 * Do not print scary warnings if the debugging
 				 * option which forces in-the-gaps is enabled.
@@ -689,7 +690,7 @@
 		c->ilebs[c->ileb_cnt++] = lnum;
 		dbg_cmt("LEB %d", lnum);
 	}
-	if (dbg_force_in_the_gaps())
+	if (dbg_is_chk_gen(c) && !(random32() & 7))
 		return -ENOSPC;
 	return 0;
 }