[CI broken] tnetdial broken again: Cannot assign requested address

[timotheecour]

#13318 fixed a recurring issue with tnetdial: Error: unhandled exception: Connection refused [OSError]

now there's another, different issue with tnetdial (IIUC, unrelated to #13318) that breaks nim CI, showing a broken build for nim:
see https://travis-ci.org/nim-lang/Nim/jobs/647511822

PASS: tests/stdlib/tnetbind.nim C                                  ( 2.32106590 secs)
FAIL: tests/stdlib/tnetdial.nim C
Test "tests/stdlib/tnetdial.nim" in category "stdlib"
Failure: reExitcodesDiffer
Expected:
exitcode: 0
Gotten:
exitcode: 1
Output:
tnetdial.nim(61)         tnetdial
tnetdial.nim(41)         test
tnetdial.nim(19)         initIPv6Server
oserr.nim(94)            raiseOSError
Error: unhandled exception: Cannot assign requested address [OSError]
PASS: tests/stdlib/tnre.nim C             PASS: lib/nimrtl.nim C --outdir:tests/dll                          ( 5.54119730 secs)

note that the error is different, so it's a different problem: Cannot assign requested address

/cc @kaushalmodi for https://gitter.im/nim-lang/Nim?at=5e3c16fe15941335585ceeb3; see also b20d7e2#commitcomment-37152517

[EDIT]

• c444ab9 disabled the test on travis but underlying problem remains