Add requirements to cover IsValidMsgId and GetPktType

**Is your feature request related to a problem? Please describe.**
Exposing CFE_SB_IsValidMsgId and CFE_SB_GetPktType needs to flow from a requirement given the current cFE requirements pattern.

**Describe the solution you'd like**
Add the requirements

**Describe alternatives you've considered**
None

**Additional context**
#263 #543

**Requester Info**
Jacob Hageman - NASA/GSFC
