Revert r177108 and restore r60506 for sparc64 as long as libstand

isn't fixed to only open the network device once and not do a open
and close dance on every file access; the firmwares of newer sparc64
machines perform an auto-negotiation with every open which in turn
causes netbooting to take horribly long if we open and close the
device over and over again.

sys/boot/common/dev_net.c

@@ -145,6 +145,9 @@ net_open(struct open_file *f, ...)
 				return (error);
 			}
 		}
+#if defined(__sparc64__)
+		netdev_opens++;
+#endif
 	}
 	netdev_opens++;
 	f->f_devdata = &netdev_sock;