add Plan 9 support

Add an implementation for Plan 9. The unit test passes with IPv4 and
IPv6.
3 jobs for up/v0.1.3 in 0 seconds (queued for 107 minutes and 19 seconds)
Status Job ID Name Coverage
  Build
failed #1551
build

 
  Test
failed #1553
allowed to fail
code_quality

failed #1552
test

 
Name Stage Failure
failed
code_quality Test There has been a timeout failure or the job got stuck. Check your timeout limits or try again
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failed
test Test There has been a timeout failure or the job got stuck. Check your timeout limits or try again
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failed
build Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
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