tests: improve spoof_ip test
tests: improve spoof_ip test

Not only check if full round trip ping (does not) work, but also if just
echo-request get filtered.

marmarek/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin