[mclagsyncd] fix out of order initialization

[globaltrouble]

What I did

Reorder class member variables.

Why I did it

I've encountered an issue with m_bufSize, it's initialization is random, some times it may be initializied with 0, some times with random value.

m_bufSize use MSG_BATCH_SIZE for initialization:

MclagLink::MclagLink(Select *select, int port) :
    MSG_BATCH_SIZE(256),
    m_bufSize(MCLAG_MAX_MSG_LEN * MSG_BATCH_SIZE),
    ...

but MSG_BATCH_SIZE declared after m_bufSize

class MclagLink : public Selectable {
  private:
    unsigned int m_bufSize;
    ...
    const int MSG_BATCH_SIZE;
    ...

so MSG_BATCH_SIZE will be initialized after m_bufSize, and m_bufSize will use MSG_BATCH_SIZE with uninitialized value.

How I verified it

Setup mclag topology, some times mclagsyncd will not be able to receive data after startup.

Details if related

More about this issue in cpp reference

IMHO it must be treated as compilation error, so it will be better to use-Werror=reorder parameter for compiler to avoid such issues.

[globaltrouble]

@gechiang could you please review?

[msosyak]

@prsunny Could we merge this?

[gechiang]

Adding @Praveen-Brcm for visibility and the compilation enabling question.
The changes look good to me. Once Praveen approves it will merge it.
Thanks!

[gechiang]

LGTM. Let's wait for @Praveen-Brcm approval before I merge this in.

[msosyak]

@Praveen-Brcm Have a look, please.

[Praveen-Brcm]

@gechiang , @akokhan @msosyak : sorry to respond late on this. I missed on it.
The changes looks good. Would like to understand if the issue is seen consistently.? We have not see such issue in Broadcom testing.

[globaltrouble]

@Praveen-Brcm it is undefined behavior, so the issue is not consistent, it is random. The issue could be easily see only when MSG_BATCH_SIZE = 0 before initialization (depends on previous data on stack). On my setup the issue seen only during first start of mclagsyncd on specific hardware.