fs/9p: Don't update file type when updating file attributes

We should only update attributes that we can change on stat2inode.
Also do file type initialization in v9fs_init_inode.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>