Merge 8d885e89a1 into e2fedeb355

The ID allows referring to a rule before it is committed, as
demonstrated in the newly added test.

I had to update all existing tests which compared generated netlink
messages against a reference, by inserting the newly added ID attribute.

rule.go

@@ -31,6 +31,7 @@ const (
 )
 
 // This constant is missing at unix.NFTA_RULE_POSITION_ID.
+// TODO: Add the constant in unix and then remove it here.
 const nfta_rule_position_id = 0xa
 
 type ruleOperation uint32