test_net does not pass on RHEL7.6
$ uname -a
Linux apollo 4.9.125-linuxkit #1 SMP Fri Sep 7 08:20:28 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
$ make check-local
make[2]: Entering directory `/builddir/build/BUILD/knot-2.8.0/tests'
CC tap/runtests.o
CCLD tap/runtests
contrib/test_base32hex..........ok
contrib/test_base64.............ok
contrib/test_dynarray...........ok
contrib/test_heap...............ok
contrib/test_net................FAILED 3, 5, 9, 11-12, 14-18, 21-23, 33, 35-48, 50-62, 68, 73-82, 84-87, 89-92, 94-97, 99-102, 104-107
...
Failed Set Fail/Total (%) Skip Stat Failing Tests
-------------------------- -------------- ---- ---- ------------------------
contrib/test_net 72/109 66% 0 0 3, 5, 9, 11-12, ..., ...
Failed 72/5958 tests, 98.79% okay, 1 test skipped.
Files=79, Tests=5958, 21.72 seconds (4.49 usr + 1.07 sys = 5.56 CPU)