Apps should check/verify msg BEFORE calling handler

[havencarlson]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I reviewed the README file to see if the feature is in the major future work.
• I performed a cursory search to see if the feature request is relevant, not redundant, nor in conflict with other tickets.

Is your feature request related to a problem? Please describe.
Copy of nasa/CS#75

The CFE core and sample app (which is supposed to be the example of "best practice") do validation on the message before calling the handler. For example:

case SAMPLE_APP_NOOP_CC:
    if (SAMPLE_APP_VerifyCmdLength(&SBBufPtr->Msg, sizeof(SAMPLE_APP_NoopCmd_t)))
    {
        SAMPLE_APP_Noop((SAMPLE_APP_NoopCmd_t *)SBBufPtr);
    }

This is different from SC, which does a similar check, but done inside each handler, for example:

SC/fsw/src/sc_cmds.c

Lines 498 to 506 in c7a3864

	void SC_NoOpCmd(const CFE_SB_Buffer_t *BufPtr)
	{
	if (SC_VerifyCmdLength(&BufPtr->Msg, sizeof(SC_NoArgsCmd_t)))
	{
	SC_OperData.HkPacket.CmdCtr++;
	CFE_EVS_SendEvent(SC_NOOP_INF_EID, CFE_EVS_EventType_INFORMATION, "No-op command. Version %d.%d.%d.%d",
	SC_MAJOR_VERSION, SC_MINOR_VERSION, SC_REVISION, SC_MISSION_REV);
	}
	}

Describe the solution you'd like
CFS Apps should follow the best practices/patterns set forth in the framework code. (there are reasons for the pattern being recommended practice)

Requester Info
Haven Carlson - NASA