DDSIRTP23 — Locator_t kind needs a reserved range and a range for vendor extensions

The Locator_t contains an integer field that identifies the type of locator. Currently only the values -1, 0, 1, 2 are defined. Which correspond to reserved values as well as UDPv4 and UDPv6.

Future revisions of the protocol may define additional kinds for things like TCP v4, TCPv6, shared memory and other transports.

At the same time vendors are using this field to identify their own custom transports.

To avoid collisions with future revisions of the protocol, the RTPS specification should reserve a range. For example, all kinds with values less than 0x00008000. These values should be reserved for future revisions of the protocol. Vendors that want to define their custom transport should use Locator_t kind with values between 0x00008000 and 0x0000FFFF (inclusive). And these values should be interpreted in the context of the RTPS vendorId so that different vendors can use the same value to mean different things.

Reserve protocol and vendor specific ranges for the Locator_t kind

To avoid future conflicts with vendor-specific Locator_t kinds, ranges have been reserved for the protocol, for vendors, and for users.
0x00000003 - 0x000001f are reserved for vendors
0x00000020 - 0x00007ffff for future use by the spec.
0x00008000-0x01FFFFFF (inclusive) for use by vendors.
0x02000000 and greater are reserved for third-party add-ons