test: mark test-net-GH-5504 as flaky on linux
test: mark test-net-GH-5504 as flaky on linux

That test can trigger a bug on some older Linux kernels.

PR-URL: https://github.com/iojs/io.js/pull/124
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node