Introduced in v5.10.0-449-gcf44ec55 it used
virshCommaStringListComplete() to generate list of options. But
this is not correct because the '--source' argument of the
'domifaddr' doesn't accept a string list (for instance
"arp,agent,lease") rather than a single string. Therefore, the
completer must return these strings separately and thus must
refrain from using virshCommaStringListComplete().

At the same time, now that we have strings we need declared as
an enum we can use TypeToString() instead of copying strings.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>