vmx: Require networkName for bridged and custom NICs

Commit 70768cda97 marked this particular config string optional, but
forgot that two of the interface types still require this name to
exist.  Mark it as optional only if there is no connectionType.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/vmx/vmx.c

@@ -2826,7 +2826,7 @@ virVMXParseEthernet(virConf *conf, int controller, virDomainNetDef **def)
         STRCASEEQ(connectionType, "bridged") ||
         STRCASEEQ(connectionType, "custom")) {
         if (virVMXGetConfigString(conf, networkName_name, &networkName,
-                                  true) < 0)
+                                  connectionType == NULL) < 0)
             goto cleanup;
     }