With ALTQ, it is possible that although the queue was not empty when we

entered the interface start function, no packets were actually dequeued.
Therefore, keep a count of how many packets we really added onto the tx
chain, and initiate a transmit only if the count is non-zero.

sys/dev/bge/if_bge.c

@@ -3201,6 +3201,7 @@ bge_start_locked(ifp)
 	struct bge_softc *sc;
 	struct mbuf *m_head = NULL;
 	u_int32_t prodidx = 0;
+	int count = 0;
 
 	sc = ifp->if_softc;
 
@@ -3247,6 +3248,7 @@ bge_start_locked(ifp)
 			ifp->if_flags |= IFF_OACTIVE;
 			break;
 		}
+		++count;
 
 		/*
 		 * If there's a BPF listener, bounce a copy of this frame
@@ -3255,6 +3257,11 @@ bge_start_locked(ifp)
 		BPF_MTAP(ifp, m_head);
 	}
 
+	if (count == 0) {
+		/* no packets were dequeued */
+		return;
+	}
+
 	/* Transmit */
 	CSR_WRITE_4(sc, BGE_MBX_TX_HOST_PROD0_LO, prodidx);
 	/* 5700 b2 errata */