Fix "IsLoopbackIp" to cover all loopback addresses; not just 127.0.0.1.

The loopback range is 127.0.0.0/8, which is everything from 127.0.0.0 to
127.255.255.255.

BUG=chromium:649118

Review-Url: https://codereview.webrtc.org/2445933003
Cr-Commit-Position: refs/heads/master@{#14807}

webrtc/base/ipaddress.cc

@@ -294,7 +294,7 @@ bool IPIsAny(const IPAddress& ip) {
 bool IPIsLoopback(const IPAddress& ip) {
   switch (ip.family()) {
     case AF_INET: {
-      return ip == IPAddress(INADDR_LOOPBACK);
+      return (ip.v4AddressAsHostOrderInteger() >> 24) == 127;
     }
     case AF_INET6: {
       return ip == IPAddress(in6addr_loopback);