Comments/document cleanup relative to SB/MSG/SBR review (and #1375)

[skliper]

Is your feature request related to a problem? Please describe.
Clarify CCSDS comment, just note CCSDS maximum is 7 bigger than int16:

cFE/modules/core_api/fsw/inc/cfe_msg_api_typedefs.h

Line 48 in c8b5e00

typedef size_t CFE_MSG_Size_t; /**< \brief Message size (CCSDS needs uint32 for max size) */

Add link to options in documentation:

cFE/modules/core_api/fsw/inc/cfe_sb.h

Line 157 in c8b5e00

** \param[in] Opts A bit field of options.

Clarify comments to eliminate implied coupling (SBN is an example use):

cFE/modules/core_api/fsw/inc/cfe_sb.h

Lines 315 to 316 in c8b5e00

	** Subscription Reporting is enabled for interprocessor communication
	** by way of the Software Bus Network (SBN) Application.

Mention CFE_SB_ReleaseMessageBuffer for the case when a message is not transmitted in CFE_SB_AllocateMessageBuffer:

cFE/modules/core_api/fsw/inc/cfe_sb.h

Line 474 in c8b5e00

** \brief Get a buffer pointer to use for "zero copy" SB sends.

Extra a in comment:

cFE/modules/core_private/fsw/inc/cfe_sbr.h

Line 52 in c8b5e00

* \brief Add a route for the given a message id

Comment in CFE_SB_UnsubscribeFull about CFE_SUCCESS status should be brought up to the else level, everything is success and explicitly mention in API documentation:

cFE/modules/sb/fsw/src/cfe_sb_api.c

Line 1264 in c8b5e00

/* Status stays CFE_SUCCESS here */

s/bush/bus:

cFE/modules/sbr/CMakeLists.txt

Line 33 in c8b5e00

message(ERROR "Invalid software bush routing implementation selected:" MISSION_MSGMAP_IMPLEMENTATION)

Fix comment, doesn't pad to boundary, instead pads to be divisible by 64 so compiler won't add padding if payload structure requires 64 bit alignment:

cFE/modules/msg/option_inc/default_cfe_msg_hdr_pri.h

Line 91 in c8b5e00

uint8 Spare[4]; /**< \brief Padding to end on 64 bit boundary */

cFE/modules/msg/option_inc/default_cfe_msg_hdr_priext.h

Line 77 in c8b5e00

uint8 Spare[4]; /**< /brief Padding to end on 64 bit boundary */

Describe the solution you'd like
Fix

Describe alternatives you've considered
None

Additional context
Code review

Requester Info
Jacob Hageman - NASA/GSFC