Increase UDP batch overhead to account for data loss metrics

[yurishkuro]

Which problem is this PR solving?

• Resolves Reporter creating batches bigger than UDP's max size #486

Short description of the changes

• Increase batch overhead constant to 70 to account for extra space occupied by data loss metrics

[codecov]

Codecov Report

Merging #488 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #488   +/-   ##
=======================================
  Coverage   88.43%   88.43%           
=======================================
  Files          59       59           
  Lines        3581     3581           
=======================================
  Hits         3167     3167           
  Misses        303      303           
  Partials      111      111

Impacted Files	Coverage Δ
transport_udp.go	97.29% <ø> (ø)	⬆️

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