feature/changelog: Fix changelog missing SETATTR entries.

Problem: Valid SETATTR entries are missing in changelog when more
         than one metadata operation happen on same inode within
         changelog roll-over time.

Cause: Metadata entries with fop num being GF_FOP_NULL are logged
       in changelog which is of no use. Since slice version
       checking is done for metadata entries to avoid logging of
       subsequent entries of same inode falling into same
       changelog, if the entry with GF_FOP_NULL is logged first,
       subsequent valid ones will be missed.

Solution: Have a boundary condition to log only those fops whose fop
          number falls between GF_FOP_NULL and GF_FOP_MAXVALUE.

BUG: 1159213
Change-Id: I128cad323afba7d33f48df1ee5e78cb829536211
Signed-off-by: Kotresh HR <khiremat@redhat.com>
Reviewed-on: http://review.gluster.org/8964
Reviewed-by: Aravinda VK <avishwan@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Venky Shankar <vshankar@redhat.com>
Tested-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/9028