Use the new MX_CHANNEL_* signal names

Change-Id: I866fa6ec135c372c717e70515c02bcc645112a9f
diff --git a/ports/fuchsia/netif/ethernetif.c b/ports/fuchsia/netif/ethernetif.c
index 24ce7d1..4a170ae 100644
--- a/ports/fuchsia/netif/ethernetif.c
+++ b/ports/fuchsia/netif/ethernetif.c
@@ -320,13 +320,13 @@
       mx_status_t r;
       mx_signals_t pending;
       r = mx_handle_wait_one(ethernetif->io.h,
-                             MX_SIGNAL_READABLE | MX_SIGNAL_PEER_CLOSED,
+                             MX_CHANNEL_READABLE | MX_CHANNEL_PEER_CLOSED,
                              MX_TIME_INFINITE, &pending);
       if (r < 0) {
         printf("ethernetif: handle wait error (%d)\n", r);
         return;
       }
-      if (pending & MX_SIGNAL_PEER_CLOSED) {
+      if (pending & MX_CHANNEL_PEER_CLOSED) {
         printf("ethernetif: handle closed\n");
         return;
       }