bugfix don't creates too large UDP packets any more

[hanyuancheung]

Fix: #2503

• Fix the bug introduced by add additional batch overhead in jaeger agent udp exporter #2489 .
• Don't creates too large UDP packets any more.

[codecov]

Codecov Report

Merging #2504 (77c781b) into main (1e4a609) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #2504   +/-   ##
=====================================
  Coverage   76.3%   76.4%           
=====================================
  Files        174     174           
  Lines      12027   12027           
=====================================
+ Hits        9184    9194   +10     
+ Misses      2598    2592    -6     
+ Partials     245     241    -4     

Impacted Files	Coverage Δ
exporters/jaeger/agent.go	77.4% <100.0%> (+6.3%)	⬆️
exporters/jaeger/uploader.go	49.2% <100.0%> (ø)
sdk/trace/batch_span_processor.go	83.4% <0.0%> (-2.1%)	⬇️
sdk/metric/sdk.go	81.5% <0.0%> (+1.4%)	⬆️
sdk/metric/refcount_mapped.go	100.0% <0.0%> (+20.0%)	⬆️