This was accomplished in xml parsing by doing away with the
stripped-down virInterfaceBareDef object, and just always using
virInterfaceDef, but with restrictions in certain places (eg, the type
of subordinate interface allowed in parsing depends on the parent
interface).

xml formatting was similarly adjusted. In addition, the formatting
functions keep track of the level of interface nesting, and insert
extra leading spaces on each line accordingly (using %*s).

The only change in formatted xml from previous (aside frmo supporting
new combinations of interface types) is that the subordinate ethernet
interfaces take up 2 lines rather than one, eg:

   <interface type='ethernet' name='eth0'>
   </interface>

instead of:

   <interface type='ethernet' name='eth0'/>

This patch updates the xml parsing and formatting, and the associated
virInterfaceDef data structure to support IPv6, along the way adding
support for multiple protocols per interface, and multiple IP
addresses per protocol.
* src/conf/interface_conf.[ch]: update the structures, code for parsing
  and serialization

The minimal XML returned from ncf_if_xml_state() doesn't contain this
attribute (which makes no sense in the case of reporting current
status of the interface), and it was preventing it from passing
through the parse/format step.

* src/conf/interface_conf.[ch]: add a new virInterfaceStartMode value
  and modify loading/saving accordingly

Rename virDomainIsActive to virDomainObjIsActive, and
virInterfaceIsActive to virInterfaceObjIsActive and finally
virNetworkIsActive to virNetworkObjIsActive.

* src/conf/domain_conf.c, src/conf/domain_conf.h,
  src/conf/interface_conf.h, src/conf/network_conf.c,
  src/conf/network_conf.h, src/lxc/lxc_driver.c,
  src/network/bridge_driver.c, src/opennebula/one_driver.c,
  src/openvz/openvz_driver.c, src/qemu/qemu_driver.c,
  src/test/test_driver.c, src/uml/uml_driver.c: Update for
  renamed APIs.

* src/capabilities.c, src/capabilities.h, src/domain_conf.c,
  src/domain_conf.h, src/domain_event.c, src/domain_event.h,
  src/interface_conf.c, src/interface_conf.h,
  src/network_conf.c, src/network_conf.h, src/node_device_conf.c,
  src/node_device_conf.h, src/secret_conf.c, src/secret_conf.h,
  src/storage_conf.c, src/storage_conf.h, src/storage_encryption_conf.c,
  src/storage_encryption_conf.h: Move to src/conf/
* src/Makefile.am: Add -Isrc/conf to the individual build targets
  which need to use XML config APIs. Remove LIBXML_CFLAGS, LIBSSH2_CFLAGS
  and SELINUX_CFLAGS from global INCLUDES and only have them in build
  targets which actually need them.  Create a libvirt_conf.la
  convenience library for all config parsers
* src/hostusb.h: Remove bogus include of domain_conf.h
* tests/Makefile.am: Add -Isrc/conf. Remove bogus -I$builddir/src
  since it never has any generated header files
* daemon/Makefile.am: Add -Isrc/conf
* proxy/Makefile.am: Add -Isrc/conf and cope with renamed files
* src/hash.c: Remove bogus include of libxml/threads.h

* qemud/remote.c src/interface_conf.[ch] src/veth.[ch]: more renaming
  from interface to iface

* interface_conf.c interface_conf.h: utilities function usful for
  interface driver like the test interface driver

* src/interface_conf.c src/interface_conf.h: the import and export
  routines and the internal APIs
* src/Makefile.am: hook the new file in the makefiles
* src/libvirt_private.syms: export a few private symbols internally
* po/POTFILES.in: the new file contains translatable strings