ocfs2/cluster: Pin the remote node item in configfs

o2net pins the node item of the remote node in configfs before initiating
the connection. It is unpinned on disconnect. This is to prevent the node
item from being unlinked while it is still in use.

Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>