x86/hvm: stop passing explicit domid to hvm_create_ioreq_server()

x86/hvm: stop passing explicit domid to hvm_create_ioreq_server()

Only in the legacy 'default server' case do we pass anything other than
current->domain->domain_id, and in that case we pass the value of
HVM_PARAM_DM_DOMAIN.

The only known user of HVM_PARAM_DM_DOMAIN is qemu-trad (and only when
compiled as a stubdom), which always sets it to DOMID_SELF (ignoring the
return value of xc_set_hvm_param) [1] and never reads it.

This patch:

- Disallows setting HVM_PARAM_DM_DOMAIN to anything other than DOMID_SELF
  and removes the call to hvm_set_dm_domain().
- Stops passing a domid to hvm_create_ioreq_server()
- Changes hvm_create_ioreq_server() to always set
  current->domain->domain_id as the domid of the emulating domain
- Removes the hvm_set_dm_domain() implementation since it is no longer
  needed.

[1] http://xenbits.xen.org/gitweb/?p=qemu-xen-traditional.git;a=blob;f=hw/xen_machine_fv.c;#l299

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>