net: fix TestInterfaceMulticastAddrs for AIX

This commit disables checkMulticastStats for AIX operating system.

Change-Id: If8d0fb609a0dcf75b7bb5c3871cfb6fad76a0a92
Reviewed-on: https://go-review.googlesource.com/c/144102
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/interface_test.go

@@ -278,7 +278,7 @@ func checkUnicastStats(ifStats *ifStats, uniStats *routeStats) error {
 
 func checkMulticastStats(ifStats *ifStats, uniStats, multiStats *routeStats) error {
 	switch runtime.GOOS {
-	case "dragonfly", "nacl", "netbsd", "openbsd", "plan9", "solaris":
+	case "aix", "dragonfly", "nacl", "netbsd", "openbsd", "plan9", "solaris":
 	default:
 		// Test the existence of connected multicast route
 		// clones for IPv4. Unlike IPv6, IPv4 multicast