This patch takes the code out of
lxcContainerRenameAndEnableInterfaces() that adds all IP addresses and
IP routes to the interface, and puts it into a utility function
virNetDevIPInfoAddToDev() in virnetdevip.c so that it can be used by
anyone.

One small change in functionality -
lxcContainerRenameAndEnableInterfaces() previously would add all IP
addresses to the interface while it was still offline, then set the
interface online, and then add the routes. Because I don't want the
utility function to set the interface online, I've moved this up so
the interface is first set online, then IP addresses and routes are
added. This is the same order that the network service from
initscripts (in ifup-ether) does it, so it shouldn't pose any problem
(and hasn't, in the tests that I've run).

There are currently two places in the domain where this combination is
used, and there is about to be another. This patch puts them together
for brevity and uniformity.

As with the newly-renamed virNetDevIPAddr and virNetDevIPRoute
objects, the new virNetDevIPInfo object will need to be accessed by a
utility function that calls low level Netlink functions (so we don't
want it to be in the conf directory) and will be called from multiple
hypervisor drivers (so it can't be in any hypervisor directory); the
most appropriate place is thus once again the util directory.

The parse and format functions are in conf/domain_conf.c because only
the domain XML (i.e. *not* the network XML) has this exact combination
of IP addresses plus routes. Note that virDomainNetIPInfoFormat() will
end up being the only caller to virDomainNetRoutesFormat() and
virDomainNetIPsFormat(), so it will just subsume those functions in a
later patch, but we can't do that until they are no longer called.

(It would have been nice to include the interface name within the
virNetDevIPInfo object (with a slight name change), but that can't
be done cleanly, because in each case the interface name is provided
in a different place in the XML relative to the routes and IP
addresses, so putting it in this object would actually make the code
more confused rather than simpler).

These functions all need to be called from a utility function that
must be located in the util directory, so we move them all into
util/virnetdevip.[ch] now that it exists.

Function and struct names were appropriately changed for the new
location, but all code is unchanged aside from motion and renaming.

This patch splits virnetdev.[ch] into multiple files, with the new
virnetdevip.[ch] containing all the functions related to setting and
retrieving IP-related info for a device (both addresses and routes).