btrfs: Add sanity check for EXTENT_DATA when reading out leaf

Add extra checks for item with EXTENT_DATA type.  This checks the
following thing:

0) Key offset
   All key offsets must be aligned to sectorsize.
   Inline extent must have 0 for key offset.

1) Item size
   Uncompressed inline file extent size must match item size.
   (Compressed inline file extent has no information about its on-disk size.)
   Regular/preallocated file extent size must be a fixed value.

2) Every member of regular file extent item
   Including alignment for bytenr and offset, possible value for
   compression/encryption/type.

3) Type/compression/encode must be one of the valid values.

This should be the most comprehensive and strict check in the context
of btrfs_item for EXTENT_DATA.

Signed-off-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ switch to BTRFS_FILE_EXTENT_TYPES, similar to what
  BTRFS_COMPRESS_TYPES does ]
Signed-off-by: David Sterba <dsterba@suse.com>

include/uapi/linux/btrfs_tree.h

@@ -732,6 +732,7 @@ struct btrfs_balance_item {
 #define BTRFS_FILE_EXTENT_INLINE 0
 #define BTRFS_FILE_EXTENT_REG 1
 #define BTRFS_FILE_EXTENT_PREALLOC 2
+#define BTRFS_FILE_EXTENT_TYPES	2
 
 struct btrfs_file_extent_item {
 	/*