Return value of XLogInsertRecord() for XLOG_SWITCH record

Hi,

I find that the return value of XLogInsertRecord() for XLOG_SWITCH record
is inconsistent with other records.

For XLOG_SWITCH record:

```
/*
* Even though we reserved the rest of the segment for us, which is
* reflected in EndPos, we return a pointer to just the end of the
* xlog-switch record.
*/
if (inserted)
{
EndPos = StartPos + SizeOfXLogRecord;
if (StartPos / XLOG_BLCKSZ != EndPos / XLOG_BLCKSZ)
{
uint64 offset = XLogSegmentOffset(EndPos, wal_segment_size);

if (offset == EndPos % XLOG_BLCKSZ)
EndPos += SizeOfXLogLongPHD;
else
EndPos += SizeOfXLogShortPHD;
}
}
```

It is equivalent to XLogBytePosToRecPtr(), but all other records use XLogBytePosToEndRecPtr().

No actual problem found yet, but I think it's better to keep them consistent. Thoughts?

--
Regards,
ChangAo Chen