smbd: DH reconnect hardening

smbd: DH reconnect hardening

Verify the smbXsrv_open_global0 is marked as disconnected. This is similarily
checked in SMB_VFS_RECONNECT() for the share_mode_entry and that catches the
problem most of the times. But to be consistent we need this check also in
smb2srv_open_recreate_fn().

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15649
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15651

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>