conf: enum cleanups in "src/conf/domain_conf.h"

conf: enum cleanups in "src/conf/domain_conf.h"

In "src/conf/domain_conf.h" there are many enumerations (enum)
declarations to be converted as a typedef too. As mentioned before,
it's better to use a typedef for variable types, function types and
other usages. I think this file has most of those enum declarations
at "src/conf/". So, me and Eric Blake plan to keep the cleanups all
over the source code. This time, most of the files changed in this
commit are related to part of one file: "src/conf/domain_conf.h".

Signed-off-by: Julio Faracco <jcfaracco@gmail.com>