Originally noticed by comparing the xml generated by virDomainSave
with the xml produced by reparsing and redumping that xml, but I
also did an audit of every last use of VIR_DOMAIN_XML_INACTIVE in
domain_conf.c to ensure that no other discrepancies exist.

* src/conf/domain_conf.c (virDomainDeviceInfoIsSet): Add
parameter, and update all callers.  Make static.
(virDomainNetDefFormat): Skip generated ifname.
(virDomainDefFormatInternal): Skip default <seclabel>.
(virDomainChrSourceDefParseXML): Skip generated pty path, and add
parameter.  Update callers.
* src/conf/domain_conf.h (virDomainDeviceInfoIsSet): Delete.
* src/libvirt_private.syms (domain_conf.h): Update.