mem: Check the XBar's port queues on functional snoops

The CoherentXBar currently doesn't check its queued slave ports when
receiving a functional snoop. This caused data corruption in cases
when a modified cache lines is forwarded between two caches.

Add the required functional calls into the queued slave ports.

src/mem/coherent_xbar.cc

@@ -832,6 +832,14 @@ CoherentXBar::recvFunctionalSnoop(PacketPtr pkt, PortID master_port_id)
                 pkt->cmdString());
     }
 
+    for (const auto& p : slavePorts) {
+        if (p->checkFunctional(pkt)) {
+            if (pkt->needsResponse())
+                pkt->makeResponse();
+            return;
+        }
+    }
+
     // forward to all snoopers
     forwardFunctional(pkt, InvalidPortID);
 }