Fix a bytebuf leak in transmission

[justinlin-linkedin]

Transmission's close method forgets to release the bytebuf.

[codecov-io]

Codecov Report

Merging #1340 into master will decrease coverage by 0.12%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #1340      +/-   ##
============================================
- Coverage     72.16%   72.04%   -0.13%     
+ Complexity     6536     6519      -17     
============================================
  Files           478      478              
  Lines         37330    37330              
  Branches       4714     4714              
============================================
- Hits          26941    26893      -48     
- Misses         9142     9175      +33     
- Partials       1247     1262      +15

Impacted Files	Coverage Δ	Complexity Δ
...in/java/com.github.ambry.network/Transmission.java	90.9% <100%> (ø)	20 <0> (ø)	⬇️
...a/com.github.ambry.network/SSLBlockingChannel.java	75.67% <0%> (-5.41%)	4% <0%> (ø)
...java/com.github.ambry.store/CompactionManager.java	89.88% <0%> (-2.98%)	25% <0%> (ø)
...github.ambry.rest/AsyncRequestResponseHandler.java	88.29% <0%> (-2.35%)	23% <0%> (ø)
...in/java/com.github.ambry.store/BlobStoreStats.java	70.41% <0%> (-2.09%)	101% <0%> (-4%)
...c/main/java/com.github.ambry.network/Selector.java	78.21% <0%> (-1.84%)	77% <0%> (-2%)
.../main/java/com.github.ambry.store/ScanResults.java	81.25% <0%> (-1.57%)	16% <0%> (-1%)
.../src/main/java/com.github.ambry.store/Journal.java	85.54% <0%> (-1.21%)	29% <0%> (-1%)
...m.github.ambry.replication/ReplicationMetrics.java	94.97% <0%> (-1.2%)	43% <0%> (-1%)
...va/com.github.ambry.replication/ReplicaThread.java	87.33% <0%> (-0.76%)	91% <0%> (-2%)
... and 7 more

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