support epoll on linux, alternative impl of PR#4493

[beiwei30]

What is the purpose of the change

alternative impl for PR #4493

Brief changelog

XXXXX

Verifying this change

XXXXX

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[codecov-io]

Codecov Report

Merging #5680 into master will increase coverage by 0.06%.
The diff coverage is 65%.

@@             Coverage Diff              @@
##             master    #5680      +/-   ##
============================================
+ Coverage     61.15%   61.22%   +0.06%     
- Complexity      421      422       +1     
============================================
  Files           923      924       +1     
  Lines         37568    37589      +21     
  Branches       5441     5446       +5     
============================================
+ Hits          22976    23015      +39     
+ Misses        12106    12077      -29     
- Partials       2486     2497      +11

Impacted Files	Coverage Δ	Complexity Δ
...e/dubbo/remoting/transport/netty4/NettyServer.java	73.52% <100%> (+0.39%)	0 <0> (ø)	⬇️
...e/dubbo/remoting/transport/netty4/NettyClient.java	71.01% <100%> (ø)	0 <0> (ø)	⬇️
...moting/transport/netty4/NettyEventLoopFactory.java	36.36% <36.36%> (ø)	0 <0> (?)
...va/org/apache/dubbo/remoting/TimeoutException.java	22.22% <0%> (-11.12%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0%> (-4.35%)	0% <0%> (ø)
...ache/dubbo/validation/filter/ValidationFilter.java	82.6% <0%> (-3.11%)	0% <0%> (ø)
...dubbo/remoting/exchange/support/DefaultFuture.java	82.88% <0%> (-2.71%)	0% <0%> (ø)
...rg/apache/dubbo/common/timer/HashedWheelTimer.java	63.1% <0%> (+0.34%)	0% <0%> (ø)	⬇️
...a/org/apache/dubbo/monitor/dubbo/DubboMonitor.java	88.57% <0%> (+1.9%)	16% <0%> (ø)	⬇️
... and 10 more

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[chickenlj]

LGTM.