For direct attach devices, in qemuBuildCommandLine, we seem to be freeing
actual device on error path (with networkReleaseActualDevice). But the actual
device is not deleted.

qemuProcessStop eventually deletes the direct attach device and releases
actual device. But by the time qemuProcessStop is called qemuBuildCommandLine
has already freed actual device, leaving stray macvtap devices behind on error.
So the simplest fix is to remove the networkReleaseActualDevice in
qemuBuildCommandLine. This patch does just that.
Signed-off-by: NRoopa Prabhu <roprabhu@cisco.com>