m/n/c/network: drop random snat mapping workaround

Linux has since fixed the issue that if two connections get assigned the
same mapped port/address combo one of them drops the packet. Instead
they just "requeue" it so it gets a new non-conflicting mapping.

This allows us the drop the workaround that mappings need to be
generated on a per-connection basis instead of just a per-port basis,
this makes Linux behave more like an endpoint-independent NAT which is
better for anything trying to establish P2P connections and also a bit
easier to debug as source ports get preserved if possible.

Change-Id: Ibfaf63746a269ec6bf0444e8c7dddb3a51b07900
Reviewed-on: https://review.monogon.dev/c/monogon/+/3907
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/node/core/network/main.go b/metropolis/node/core/network/main.go
index 8b834ac..f9fa010 100644
--- a/metropolis/node/core/network/main.go
+++ b/metropolis/node/core/network/main.go
@@ -296,10 +296,7 @@
 				Register: 8,
 				Data:     binaryutil.NativeEndian.PutUint32(node.LinkGroupClusternet),
 			},
-			&expr.Masq{
-				FullyRandom: true,
-				Persistent:  true,
-			},
+			&expr.Masq{},
 		},
 	})