Avoid deprecated EpollEventLoopGroup usage

Replaces EpollEventLoopGroup with MultiThreadIoEventLoopGroup configured
via EpollIoHandler factory.

This aligns with the Netty 5 IO handler architecture and
avoids usage of deprecated epoll transport APIs.

Signed-off-by: Andrey Litvitski <[email protected]>

Author: therepanic

spring-grpc-core/src/main/java/org/springframework/grpc/client/NettyGrpcChannelFactory.java

@@ -20,14 +20,16 @@
 
 import io.grpc.ChannelCredentials;
 import io.grpc.netty.NettyChannelBuilder;
+import io.netty.channel.MultiThreadIoEventLoopGroup;
 import io.netty.channel.epoll.EpollDomainSocketChannel;
-import io.netty.channel.epoll.EpollEventLoopGroup;
+import io.netty.channel.epoll.EpollIoHandler;
 import io.netty.channel.unix.DomainSocketAddress;
 
 /**
  * {@link GrpcChannelFactory} that creates Netty-based gRPC channels.
  *
  * @author Chris Bono
+ * @author Andrey Litvitski
  */
 public class NettyGrpcChannelFactory extends DefaultGrpcChannelFactory<NettyChannelBuilder> {
 
@@ -48,7 +50,7 @@ protected NettyChannelBuilder newChannelBuilder(String target, ChannelCredential
 			target = target.substring(5);
 			return NettyChannelBuilder.forAddress(new DomainSocketAddress(target))
 				.channelType(EpollDomainSocketChannel.class)
-				.eventLoopGroup(new EpollEventLoopGroup());
+				.eventLoopGroup(new MultiThreadIoEventLoopGroup(EpollIoHandler.newFactory()));
 		}
 		return NettyChannelBuilder.forTarget(target, credentials);
 	}