ceph: single workqueue for inode related works

ceph: single workqueue for inode related works

BugLink: https://bugs.launchpad.net/bugs/1834235
We have three workqueue for inode works. Later patch will introduce
one more work for inode. It's not good to introcuce more workqueue
and add more 'struct work_struct' to 'struct ceph_inode_info'.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit 1cf89a8dee5e6e9d4fcb81b571a54d40068dfbb7)
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>