DDSIRTP25 — Address deferred issue: Inclusion of Message Size & CRC as part of DDSI/RTPS Messages

The following issue https://issues.omg.org/browse/DDSIRTP23-6 was deferred in the last RTF so it should have been moved to this RTF. Since it didn't happen automatically we are entering this issue manually here.

For details on the previous discussion and what was proposed as a resolution see DDSIRTP23-6.

Overall Approach
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Introduce a new RTPS submessage "RTPSHeaderExtension" with the following elements:

• messageLength

The messageLength indicates the length of the RTPS message
The rtpsSendTimestamp indicates the time when the message was sent
The messageChecksum

Mechanisms to add additional information in future revisions.

The RTPSHeaderExtension submessage, if present, shall follow immediately after the RTPS Header

The DDS Security specification will leave this RTPSHeaderExtension following the RTPS Header and before the SecureRTPSPrefixSubMsg. The length will be updated to the new length after processing by the security plugins.

Add CRC support via a HeaderExtension submessage

Introduce a new RTPS submessage "RTPSHeaderExtension" with the following elements:

• rtpsMsgLength (indicates the length of the RTPS message)
• rtpsPort (destination port for submessage)
• rtpsChecksum (message checksum)

The RTPSHeaderExtension submessage, if present, shall follow immediately after the RTPS Header.