Fix missing return in test function causing SIGILL with GCC 14

[yxieca]

Description

MuxManagerTest::setUseWellKnownMacActiveActive() is declared as returning bool but has no return statement. This is undefined behavior in C++.

• GCC 13 (bookworm): Silently ignores the missing return
• GCC 14 (trixie): Inserts ud2 (intentional illegal instruction) to trap the UB

This causes MuxManagerTest.ServerMacActiveActiveBeforeLinkProberInit to crash with SIGILL (exit code 132) when linkmgrd is built in a trixie environment.

Root Cause

// test/MuxManagerTest.cpp:118
bool MuxManagerTest::setUseWellKnownMacActiveActive(bool use)
{
    mMuxManagerPtr->setUseWellKnownMacActiveActive(use);
    // No return statement — UB!
}

The underlying MuxManager::setUseWellKnownMacActiveActive() returns void, so the test wrapper should too.

Fix

Change return type from bool to void in both the declaration (.h) and definition (.cpp).

How I tested

• Built linkmgrd test binary with -g -O0 in trixie slave container
• Ran under GDB: crash at ud2 instruction at function epilogue
• After fix: function no longer has missing return UB

[mssonicbld]

/azp run

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[mssonicbld]

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