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.

Change-Id: Iff585ea573ac5e521a361541c6646225943f0b2d
BUG: 1104954
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>