ksmbd: share SMB2 lease state across opens

Model SMB2 leases as per-client/per-key objects instead of keeping a
separate lease copy in every oplock_info.  The lease table now stores
lease objects and each lease tracks the opens that reference it.

This makes same ClientGuid/LeaseKey opens observe a single lease state,
so lease upgrades, breaks, ACKs, and close teardown do not diverge across
per-open copies.  Keep one reference for the lease table entry and one
reference for each open, and remove the table entry when the last open is
detached.

Update lease break ACK handling to refresh all open oplock levels from
the shared lease state.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

Author: namjaejeon