[Task] Prevent multiple SNP shutdown and reinitialization invocations

[makubacki]

NetLibDetectMediaWaitTimeout() in DxeNetLib is called 15 places in the codebase. Multiple callers might call into the function for the same NIC such as Dhcp4Dxe, PxeBcDxe, etc. For example:

  Snp->undi.initialize()  <-- By SimpleNetworkDriverStart

  Snp->undi.initialize()   <-- By NetLibDetectMedia()
  Snp->undi.initialize()  8000h:6h
  Snp->undi.initialize()

  Snp->undi.initialize()  <-- By NetLibDetectMedia()
  Snp->undi.initialize()  8000h:6h
  Snp->undi.initialize()

Initialization might also occur multiple times in the same flow, for example, when SnpUndi32Initialize() first calls with PXE_OPFLAGS_INITIALIZE_DETECT_CABLE and if that fails, again with PXE_OPFLAGS_INITIALIZE_DO_NOT_DETECT_CABLE:

mu_basecore/NetworkPkg/SnpDxe/Initialize.c

Lines 254 to 277 in c4a845c

	//
	// If UNDI support cable detect for INITIALIZE command, try it first.
	//
	if (Snp->CableDetectSupported) {
	if (PxeInit (Snp, PXE_OPFLAGS_INITIALIZE_DETECT_CABLE) == EFI_SUCCESS) {
	goto ON_EXIT;
	}
	}
	Snp->Mode.MediaPresent = FALSE;
	EfiStatus = PxeInit (Snp, PXE_OPFLAGS_INITIALIZE_DO_NOT_DETECT_CABLE);
	if (EFI_ERROR (EfiStatus)) {
	gBS->CloseEvent (Snp->Snp.WaitForPacket);
	goto ON_EXIT;
	}
	//
	// Try to update the MediaPresent field of EFI_SIMPLE_NETWORK_MODE if the UNDI support it.
	//
	if (Snp->MediaStatusSupported) {
	PxeGetStatus (Snp, NULL, FALSE);
	}

Collectively this can lead to SNP shutting down and reinitializing multiple times when it might not need to impacting stability and performance.

---

This issue tracks exploration of a solution to reduce the number of times shutdown and reinitialization occurs across the network stack.

[makubacki]

@wenbhou is going to look into this issue (he can't be assigned directly).

[makubacki]

I was able to take care of this in #1636. NetLibDetectSnpMediaWithTimeoutInternal() is guarded with TPL (TPL_CALLBACK) so it runs sequentially. Media gets detected properly the first time. Subsequent checks simply return EFI_SUCCESS as expected.