runtime: correct test for when to poll network

Fixes #6610.

R=golang-dev, khr
CC=golang-dev
https://golang.org/cl/14793043

src/pkg/runtime/proc.c

@@ -2382,7 +2382,7 @@ sysmon(void)
 		// poll network if not polled for more than 10ms
 		lastpoll = runtime·atomicload64(&runtime·sched.lastpoll);
 		now = runtime·nanotime();
-		if(lastpoll != 0 && lastpoll + 10*1000*1000 > now) {
+		if(lastpoll != 0 && lastpoll + 10*1000*1000 < now) {
 			runtime·cas64(&runtime·sched.lastpoll, lastpoll, now);
 			gp = runtime·netpoll(false);  // non-blocking
 			if(gp) {