The qemu driver accesses fields in the virDomainNetDef directly, but
with the advent of the virDomainActualNetDef, some pieces of
information may be found in a different place (the ActualNetDef) if
the network connection is of type='network' and that network is of
forward type='bridge|private|vepa|passthrough'. The previous patch
added functions to mask this difference from callers - they hide the
decision making process and just pick the value from the proper place.

This patch uses those functions in the qemu driver as a first step in
making qemu work with the new network types. At this point, the
virDomainActualNetDef is guaranteed always NULL, so the GetActualX()
function will return exactly what the def->X that's being replaced
would have returned (ie bisecting is not compromised).

There is one place (in qemu_driver.c) where the internal details of
the NetDef are directly manipulated by the code, so the GetActual
functions cannot be used there without extra additional code; that
file will be treated in a separate patch.