Coverity notes that ->ifname is used after the VIR_FREE done in the
code path after the call to virNetDevMacVLanDeleteWithVPortProfile
by a call to virNetDevOpenvswitchRemovePort.

Since the ->ifname will be VIR_FREE()'d eventually in virDomainNetDefFree
just remove the extraneous VIR_FREE here.

When originally added, the Openvswitch code wasn't present and checks
were made for non NULL prior to use.