[Data-Plane Mgr] Fix missing subnet entity in multicast GoalState

[xieus]

Bug Description

Each port creation generates one unicast GS and one multicast GS. In current implementation, multicast GS only includes neighbor states while lacks of corresponding subnet states. This causes ACA failure to look up neighbor.

This PR proposes a simple fix to add those missing subnet entities, and enable debug-level logging to show GS detail before sending it to ACA.

[codecov-io]

Codecov Report

Merging #564 (59bebf1) into master (c7baf54) will increase coverage by 0.02%. The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #564      +/-   ##
============================================
+ Coverage     34.38%   34.40%   +0.02%     
- Complexity     1236     1241       +5     
============================================
  Files           501      501              
  Lines         12398    12398              
  Branches       1567     1567              
============================================
+ Hits           4263     4266       +3     
+ Misses         7557     7555       -2     
+ Partials        578      577       -1     

Impacted Files	Coverage Δ	Complexity Δ
...com/futurewei/alcor/macmanager/utils/MacUtils.java	56.52% <0.00%> (-8.70%)	7.00% <0.00%> (-1.00%)
...alcor/elasticipmanager/dao/ElasticIpAllocator.java	63.81% <0.00%> (+0.27%)	49.00% <0.00%> (+1.00%)
...rewei/alcor/portmanager/processor/PortContext.java	71.62% <0.00%> (+2.70%)	33.00% <0.00%> (+2.00%)
...i/alcor/portmanager/processor/RouterProcessor.java	85.29% <0.00%> (+5.88%)	10.00% <0.00%> (+1.00%)

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