Refactored SCMP for non-blocking send

[tzaeschke]

Provide non-blocking send for echo and traceroute

[codecov]

Codecov Report

Attention: Patch coverage is 83.95604% with 73 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/main/java/org/scion/jpan/ScmpSenderAsync.java	85.23%	20 Missing and 11 partials ⚠️
src/main/java/org/scion/jpan/ScmpResponder.java	80.68%	10 Missing and 7 partials ⚠️
src/main/java/org/scion/jpan/ScmpSender.java	83.80%	12 Missing and 5 partials ⚠️
src/main/java/org/scion/jpan/Scmp.java	76.92%	6 Missing ⚠️
.../main/java/org/scion/jpan/internal/ScmpParser.java	92.30%	1 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ	Complexity Δ
...n/java/org/scion/jpan/AbstractDatagramChannel.java	83.40% <ø> (ø)	75.00 <0.00> (ø)
src/main/java/org/scion/jpan/ScmpChannel.java	84.21% <ø> (ø)	18.00 <0.00> (ø)
src/main/java/org/scion/jpan/internal/Util.java	50.00% <ø> (ø)	1.00 <0.00> (?)
.../main/java/org/scion/jpan/internal/ScmpParser.java	88.23% <92.30%> (+2.52%)	10.00 <3.00> (+3.00)
src/main/java/org/scion/jpan/Scmp.java	86.81% <76.92%> (-1.80%)	7.00 <3.00> (+3.00)	⬇️
src/main/java/org/scion/jpan/ScmpResponder.java	80.68% <80.68%> (ø)	8.00 <8.00> (?)
src/main/java/org/scion/jpan/ScmpSender.java	83.80% <83.80%> (ø)	10.00 <10.00> (?)
src/main/java/org/scion/jpan/ScmpSenderAsync.java	85.23% <85.23%> (ø)	18.00 <18.00> (?)

... and 1 file with indirect coverage changes