Fix a bug which could lead to receive side lockup when WC is disabled.

When submitting rx buffers and not using WC fifo, always replace the
invalid DMA address with the real one, otherwise allocation failures
could lead to the invalid DMA address being given to the NIC, and
that would cause the receive side to lockup.

sys/dev/mxge/if_mxge.c

@@ -1736,6 +1736,7 @@ mxge_submit_8rx(volatile mcp_kreq_ether_recv_t *dst,
 	mb();
 	mxge_pio_copy(dst + 4, src + 4, 4 * sizeof (*src));
 	mb();
+	src->addr_low = low;
 	dst->addr_low = low;
 	mb();
 }