[NTFS] - Restructure some code in preparation for the next commit:

-SetAttributeDataLength() has been split into two functions, SetNonResidentAttributeDataLength() and SetResidentAttributeDataLength(). This should improve code readibility and allows for resizing an attribute when there's no FileObject associated with it.
-Added "MftDataOffset" member to DEVICE_EXTENSION, which stores the offset of the Mft's $DATA attribute. (I'm starting to think it's better to add a member for offset to NTFS_ATTR_CONTEXT directly, but I'll save that level of restructuring for a future commit.)

svn path=/branches/GSoC_2016/NTFS/; revision=75055

drivers/filesystems/ntfs/ntfs.h

@@ -116,6 +116,7 @@ typedef struct
 
     NTFS_INFO NtfsInfo;
 
+    ULONG MftDataOffset;
     ULONG Flags;
     ULONG OpenHandleCount;
 
@@ -869,6 +870,20 @@ SetFileRecordEnd(PFILE_RECORD_HEADER FileRecord,
                  PNTFS_ATTR_RECORD AttrEnd,
                  ULONG EndMarker);
 
+NTSTATUS
+SetNonResidentAttributeDataLength(PDEVICE_EXTENSION Vcb,
+                                  PNTFS_ATTR_CONTEXT AttrContext,
+                                  ULONG AttrOffset,
+                                  PFILE_RECORD_HEADER FileRecord,
+                                  PLARGE_INTEGER DataSize);
+
+NTSTATUS
+SetResidentAttributeDataLength(PDEVICE_EXTENSION Vcb,
+                               PNTFS_ATTR_CONTEXT AttrContext,
+                               ULONG AttrOffset,
+                               PFILE_RECORD_HEADER FileRecord,
+                               PLARGE_INTEGER DataSize);
+
 ULONGLONG
 AttributeAllocatedLength(PNTFS_ATTR_RECORD AttrRecord);