Feat linux firewall support (#805)

Update the client's engine to apply firewall rules received from the manager (results of ACL policy).

client/firewall/nftables/rule_linux.go

@@ -0,0 +1,16 @@
+package nftables
+
+import (
+	"github.com/google/nftables"
+)
+
+// Rule to handle management of rules
+type Rule struct {
+	*nftables.Rule
+	id string
+}
+
+// GetRuleID returns the rule id
+func (r *Rule) GetRuleID() string {
+	return r.id
+}