f2fs: introduce CONFIG_F2FS_CHECK_FS for BUG_ON control

This config will support an option to remove so many BUG_ONs that degrade
the performance potentially.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/Kconfig

@@ -63,3 +63,11 @@ config F2FS_FS_SECURITY
 	  the extended attribute support in advance.
 
 	  If you are not using a security module, say N.
+
+config F2FS_CHECK_FS
+	bool "F2FS consistency checking feature"
+	depends on F2FS_FS
+	help
+	  Enables BUG_ONs which check the file system consistency in runtime.
+
+	  If you want to improve the performance, say N.