virDomainChrDefParseTargetXML: Use virXMLProp*
virDomainChrDefParseTargetXML: Use virXMLProp*

This strictens the parser to disallow negative values (interpreted as
`UINT_MAX + value + 1`) for attribute `port`. Allowing negative
numbers to be interpreted this way makes no sense for this attribute.

Signed-off-by: Tim Wiederhake <da93ee425e056cfcf1ddac9fc87851b25464abf4@redhat.com>
Reviewed-by: Laine Stump <c23361c43fbf79fed83e8b76173707b083d6caf5@redhat.com>

olafhering/libvirt,olafhering/libvirt,nertpinx/libvirt,nertpinx/libvirt,libvirt/libvirt,nertpinx/libvirt,jfehlig/libvirt,jfehlig/libvirt,jfehlig/libvirt,jfehlig/libvirt,nertpinx/libvirt,crobinso/libvirt,zippy2/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,crobinso/libvirt,libvirt/libvirt,crobinso/libvirt,libvirt/libvirt,crobinso/libvirt,nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,olafhering/libvirt