DDSIRTP23 — Clarify start of alignment for SerializedPayload

Section 9.4.2.12 should clearly state where the alignment begins. Is it before the encapsulation header or after the encapsulation header?

Note that 9.4.2.11 already talks about it for the ParameterList encapsulation so 9.4.2.12 should use the same approach.

The language in 9.4.2.11 should also be improved to make it less ambiguous, specifically stating that the reset of the alignment occurs after the parameterID before the parameter data is serialized.

Clarify the start alignment for the SerializedPayload SubmessageElement

The SerializedPayload SubmessageElement has been updated to clearly state that the CDR stream is logically reset after the encapsulation header, similar to what is already described in section 9.4.2.11. Section 9.4.2.11 has also been improved for clarity, with no change to semantics.