util/socketpair_ersatz test requires configured network

When I use unshare -r -n ./src/test/test to try to reproduce legacy/trac#30409 (moved), I get this error:

util/socketpair_ersatz: [forking] 
  FAIL src/test/test_util.c:5402: assert(0 OP_EQ socketpair_result): 0 vs -101
  [socketpair_ersatz FAILED]