bhyve: do not cleanup unallocated networks on fail

virBhyveProcessStart() calls bhyveNetCleanup() if it fails. However,
it might fail earlier than networks are allocated, so modify
bhyveNetCleanup() to check if net->ifname is not NULL before
going further with the cleanup.

src/bhyve/bhyve_process.c

@@ -78,6 +78,7 @@ bhyveNetCleanup(virDomainObjPtr vm)
         int actualType = virDomainNetGetActualType(net);
 
         if (actualType == VIR_DOMAIN_NET_TYPE_BRIDGE) {
+            if (net->ifname) {
                 ignore_value(virNetDevBridgeRemovePort(
                                 virDomainNetGetActualBridgeName(net),
                                 net->ifname));
@@ -85,6 +86,7 @@ bhyveNetCleanup(virDomainObjPtr vm)
             }
         }
     }
+}
 
 int
 virBhyveProcessStart(virConnectPtr conn,