nl-cache: Resolve the inode is not of type dir error

[mohit84]

During fop(mkdir)_cbk process by nl-cache it checks the inode type validation based on loc->inode though loc->inode is populated by first xlator like fuse/gfapi. The loc->inode does not have inode_type so it always throw an error.

Solution: Check the inode type based on inode attribute return by server xlator as an argument in callback function.

Fixes: #2521 Change-Id: Ibc4675ebe095d14310cdb2348c2f55a73f972046