bump google/nftables to v0.3.0

Set NAT.Specified on DNAT with a port so compiled exprs match kernel readback.

internal/nftables/compiler.go

@@ -563,6 +563,7 @@ func (c *Compiler) compileDNATRule(state *FirewallState, tag, srcZone, srcAddr,
 						)
 						natExpr.RegProtoMin = 2
 						natExpr.RegProtoMax = 2
+						natExpr.Specified = true
 					}
 					exprs = append(exprs, natExpr)
 				} else {
@@ -583,6 +584,7 @@ func (c *Compiler) compileDNATRule(state *FirewallState, tag, srcZone, srcAddr,
 						)
 						natExpr.RegProtoMin = 2
 						natExpr.RegProtoMax = 2
+						natExpr.Specified = true
 					}
 					exprs = append(exprs, natExpr)
 				}

internal/nftables/compiler_test.go

@@ -456,15 +456,19 @@ func TestCompile_DNAT(t *testing.T) {
 		t.Fatalf("Compile() error: %v", err)
 	}
 
-	found := false
+	var nat *expr.NAT
 	for _, r := range state.Rules["prerouting"] {
 		if r.Tag == "rule:0" {
-			found = true
+			nat, _ = r.Exprs[len(r.Exprs)-1].(*expr.NAT)
 			break
 		}
 	}
-	if !found {
-		t.Error("no DNAT rule found in prerouting chain")
+	if nat == nil {
+		t.Fatal("no DNAT rule found in prerouting chain")
+	}
+	// The kernel reports PROTO_SPECIFIED whenever a port register is set.
+	if nat.RegProtoMin != 2 || !nat.Specified {
+		t.Errorf("DNAT with port must set RegProtoMin and Specified to match kernel readback, got %+v", nat)
 	}
 }