libxl: Move domain_create_info_setdefault earlier

libxl: Move domain_create_info_setdefault earlier

We need this before we start to figure out the passthrough mode.

I have checked that nothing in libxl__domain_create_info_setdefault
nor the two implementations of ..._arch_... accesses anything else,
other than (i) the domain type (which this function is responsible for
setting and nothing before it looks at) (ii) c_info->ssidref (which is
defaulted by flask code near the top of
libxl__domain_config_setdefault and not accessed afterwards).

So no functional change.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>