DDSIRTP21 — Add implementation note on not serializing redundant info in builtin topic

Simple discovery data has parameters containing redundant information. To not waste bandwidth, implementations should be able to refrain from sending redundant information. As such, the spec should include an implementation note on this matter.
Resolution:
Add text in PSM, Section 9.6.2.2 describing the general allowable case in which implementations may avoid serializing parameters with redundant information.
Revised Text:
Add to Section 9.6.2.2, right before section 9.6.2.2.1 the following paragraph::

For optimization, implementations of the protocol may refrain from include in the Data submessage a parameter if it contains information that is redundant with parameters present in that same Data submessage. As a result of this optimization an implementation can omit the serialization of the parameters listed in - ParameterId subspaces- ParameterId subspaces

Table 9.1 - ParameterId subspaces
BuiltinEndpoint Parameter which may be omitted Parameter where the information on the omitted parameter can be found
SPDPdiscoveredParticipantData ParticipantProxy::guidPrefix ParticipantBuiltinTopicData::key

DiscoveredReaderData ReaderProxy::remoteReaderGuid SubscriptionBuiltinTopicData::key

DiscoveredWriterData ReaderProxy::remoteWriterGuid PublicationBuiltinTopicData::key
.
For example, an implementation of the protocol sending DATA message containing the SPDPdiscoveredParticipantData may omit the parameter that contains the guidPrefix. If the guidPrefix is not present in the DATA message, the implementation of the protocol in the receiver side must derive this value from the "key" parameter which is always present in the DATA message.

Add text in PSM, Section 9.6.2.2 describing the general allowable case in which implementations may avoid serializing parameters with redundant information.