Optimize code in RoundRobinLoadBalance

[Horanol]

What is the purpose of the change

Optimize code in RoundRobinLoadBalance

[codecov-io]

Codecov Report

Merging #4604 into master will decrease coverage by 0.05%.
The diff coverage is 66.66%.

@@             Coverage Diff              @@
##             master    #4604      +/-   ##
============================================
- Coverage     64.17%   64.12%   -0.06%     
+ Complexity      453      452       -1     
============================================
  Files           768      768              
  Lines         32869    32863       -6     
  Branches       5179     5177       -2     
============================================
- Hits          21094    21073      -21     
- Misses         9358     9372      +14     
- Partials       2417     2418       +1

Impacted Files	Coverage Δ	Complexity Δ
...rpc/cluster/loadbalance/RoundRobinLoadBalance.java	79.31% <66.66%> (-0.38%)	0 <0> (ø)
.../apache/dubbo/qos/protocol/QosProtocolWrapper.java	64.1% <0%> (-17.95%)	0% <0%> (ø)
.../remoting/transport/netty4/NettyServerHandler.java	61.9% <0%> (-9.53%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	58.69% <0%> (-8.7%)	0% <0%> (ø)
...ng/transport/dispatcher/all/AllChannelHandler.java	51.42% <0%> (-5.72%)	0% <0%> (ø)
...ng/exchange/support/header/HeartbeatTimerTask.java	73.68% <0%> (-5.27%)	0% <0%> (ø)
.../org/apache/dubbo/remoting/ExecutionException.java	15.78% <0%> (-5.27%)	0% <0%> (ø)
...exchange/support/header/HeaderExchangeHandler.java	64.75% <0%> (-2.46%)	0% <0%> (ø)
...ache/dubbo/registry/multiple/MultipleRegistry.java	62.67% <0%> (-0.71%)	20% <0%> (-1%)
...he/dubbo/registry/multicast/MulticastRegistry.java	69.68% <0%> (+1.8%)	0% <0%> (ø)	⬇️
... and 2 more

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[CLAassistant]

All committers have signed the CLA.

[chickenlj]

Sorry, but the RoundRobin implementation has been refactorred