gfapi: link inodes in relevant entry FOPs

Do not let inode linking to happen only in lookup(). While
that works, it is inefficient.

Change-Id: I51bbfb6255ec4324ab17ff00566375f49d120c06
BUG: 953694
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/4931
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>