Relax the specification for java.net.NetPermission to explicitly allow other named permissions to be used.

The current specification of this classes states: "The following table lists all the possible NetPermission target names ...", which implies that unless the permission target is listed in the table, it cannot be used.

However, there is no such enforcement in the implementation, and it is useful and somewhat common for applications / libraries to create their own permission target names.

( similar to JDK-8077055)