SCMP echo problems, see #96

[tzaeschke]

SCMP echo problems, see #96.
This PR does not resolve the issue but clears up some other problems

[codecov]

Codecov Report

Attention: Patch coverage is 21.05263% with 15 lines in your changes missing coverage. Please review.

Files	Coverage Δ	Complexity Δ
src/main/java/org/scion/jpan/PathMetadata.java	47.14% <ø> (ø)	12.00 <0.00> (ø)
src/main/java/org/scion/jpan/ScmpChannel.java	85.14% <100.00%> (+0.93%)	18.00 <0.00> (ø)
src/main/java/org/scion/jpan/ScionService.java	66.40% <0.00%> (-1.36%)	49.00 <0.00> (ø)
src/main/java/org/scion/jpan/ScionUtil.java	90.10% <0.00%> (-5.24%)	29.00 <0.00> (ø)
...ava/org/scion/jpan/internal/ScionBootstrapper.java	75.65% <0.00%> (-2.58%)	29.00 <0.00> (ø)