USB: Do not wait for first explore in Stack constructor.

Following various refactors, at the point the Stack object is created,
there are no bus managers yet, so exploring will find nothing.

src/add-ons/kernel/bus_managers/usb/Stack.cpp

@@ -19,7 +19,6 @@
 
 Stack::Stack()
 	:	fExploreThread(-1),
-		fFirstExploreDone(false),
 		fExploreSem(-1),
 		fAllocator(NULL),
 		fObjectIndex(1),
@@ -59,12 +58,6 @@ Stack::Stack()
 	fExploreThread = spawn_kernel_thread(ExploreThread, "usb explore",
 		B_LOW_PRIORITY, this);
 	resume_thread(fExploreThread);
-
-	// wait for the first explore to complete. this ensures that a driver that
-	// is opening the module does not get rescanned while or before installing
-	// its hooks.
-	while (!fFirstExploreDone)
-		snooze(10000);
 }
 
 
@@ -210,7 +203,7 @@ Stack::ExploreThread(void *data)
 	Stack *stack = (Stack *)data;
 
 	while (acquire_sem_etc(stack->fExploreSem, 1, B_RELATIVE_TIMEOUT,
-		USB_DELAY_HUB_EXPLORE) != B_BAD_SEM_ID) {
+			USB_DELAY_HUB_EXPLORE) != B_BAD_SEM_ID) {
 		stack->Explore();
 	}
 
@@ -250,7 +243,6 @@ Stack::Explore()
 		changeItem = next;
 	}
 
-	fFirstExploreDone = true;
 	mutex_unlock(&fExploreLock);
 	RescanDrivers(rescanList);
 }

src/add-ons/kernel/bus_managers/usb/usb_private.h

@@ -183,7 +183,6 @@ static	int32							ExploreThread(void *data);
 
 		Vector<BusManager *>			fBusManagers;
 		thread_id						fExploreThread;
-		bool							fFirstExploreDone;
 		sem_id							fExploreSem;
 
 		mutex							fStackLock;