libxl: domain save: rename variables etc.

libxl: domain save: rename variables etc.

Preparatory work for making domain suspend asynchronous:

* Rename `struct suspendinfo' to `libxl__domain_suspend_state'
  and move it to libxl_internal.h.

* Rename variables `si' to `dss'.

* Change the stack-allocated state and callbacks from
    struct suspendinfo si;
    struct save_callbacks callbacks;
    struct restore_callbacks callbacks;
  to
    libxl__domain_suspend_state dss[1];
    struct save_callbacks callbacks[1];
    struct restore_callbacks callbacks[1];
  so that it may be referred to as a pointer variable everywhere.

* Rename the variable `flags' (in libxl__domain_suspend_state) to
  `xcflags', to help distinguish it from the other `flags' which is
  passed in from the calling application in libxl_domain_suspend_info.
  Abolish the local variable in libxl__domain_suspend_common, as it
  can use the one in the dss.

* Move the prototypes of suspend-related functions in libxl_internal.h
  to after the definition of the state struct.

* Replace several ctx variables with gc variables and
  consequently references to ctx with CTX.  Change references
  to `dss->gc' in the functional code to simply `gc'.

* Use LOG* rather than LIBXL__LOG* in a number of places.

* In libxl__domain_save_device_model use `rc' instead of `ret'.

* Introduce and use `gc' and `domid' in
  libxl__domain_suspend_common_callback.

* Wrap some long lines.

* Add an extra pair of parens for clarity in a flag test.

* Remove two pointless casts from void* to a struct*.

No functional change whatsoever.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>