smbd: ignore SVHDX create context

smbd: ignore SVHDX create context

According to discussions with dochelp@microsoft.com, an SMB
server should ignore an SVHDX_OPEN_DEVICE_CONTEXT or
SVHDX_OPEN_DEVICE_CONTEXT_V2 create context if it does not
support the RSVD protocol. This is contrary to [MS-SMB2] rev 48.0
which states (3.3.5.9.14) that the open should fail in this case.

Failing the create fails Windows backup if the SMB dialect is
SMB3.0.2 or higher.

Hopefully a new revision of MS-SMB2 will clear this up in the future.

Meanwhile, this patch modifies smbd to ignore the
SVHDX_OPEN_DEVICE_CONTEXT by default. This can be overriden by a VFS
module if a VFS module adds support for RSVD.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11753

Signed-off-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Richard Sharpe <realrichardsharpe@gmail.com>