Close delegate resolver from RoundRobinInetAddressResolver (#9214)

Motivation:

RoundRobinDnsAddressResolverGroup ultimately opens UDP
ports for DNS resolution. Callers likely expect that
RoundRobinDnsAddressResolverGroup#close() will close those
ports, but that is not currently true (see #9212).

Modifications:

Overrode RoundRobinInetAddressResolver#close() to close
the delegate name resolver, which in turn closes any UDP
ports used for name resolution.

Result:

RoundRobinDnsAddressResolverGroup#close() closes UDP ports
as expected. This fixes #9212.

resolver/src/main/java/io/netty/resolver/RoundRobinInetAddressResolver.java

@@ -100,4 +100,9 @@ public class RoundRobinInetAddressResolver extends InetNameResolver {
     private static int randomIndex(int numAddresses) {
         return numAddresses == 1 ? 0 : PlatformDependent.threadLocalRandom().nextInt(numAddresses);
     }
+
+    @Override
+    public void close() {
+        nameResolver.close();
+    }
 }