polish attributes of GRPCChannelConfiguration

src/objective-c/GRPCClient/private/GRPCChannelPool.h

@@ -31,8 +31,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 @interface GRPCChannelConfiguration : NSObject<NSCopying>
 
-@property(atomic, strong, readwrite) NSString *host;
-@property(atomic, strong, readwrite) GRPCCallOptions *callOptions;
+@property(copy, readonly) NSString *host;
+@property(strong, readonly) GRPCCallOptions *callOptions;
 
 @property(readonly) id<GRPCChannelFactory> channelFactory;
 @property(readonly) NSMutableDictionary *channelArgs;

src/objective-c/GRPCClient/private/GRPCChannelPool.m

@@ -141,9 +141,7 @@ const NSTimeInterval kChannelDestroyDelay = 30;
 }
 
 - (nonnull id)copyWithZone:(nullable NSZone *)zone {
-  GRPCChannelConfiguration *newConfig = [[GRPCChannelConfiguration alloc] init];
-  newConfig.host = _host;
-  newConfig.callOptions = _callOptions;
+  GRPCChannelConfiguration *newConfig = [[GRPCChannelConfiguration alloc] initWithHost:_host callOptions:_callOptions];
 
   return newConfig;
 }