test: netns: Use passthru mode for MACVLANs

This mode let's us receive all packets from the parent device, which
is automatically set in promiscuous mode, and let's the MACVLAN
transmit packets with any SA, which we need to implement a TPMR (or a
bridge or anything else we might dream up)

test/infamy/netns.py

@@ -59,7 +59,7 @@ class IsolatedMacVlans:
                                 "link", parent,
                                 "address", self._stable_mac(parent),
                                 "netns", str(self.sleeper.pid),
-                                "type", "macvlan"], check=True)
+                                "type", "macvlan", "mode", "passthru"], check=True)
                 self.runsh(f"""
                 while ! ip link show dev {ifname}; do
                     sleep 0.1