rule: populate Type field in RuleList and RuleListFiltered

The Rule.Type field was missing from the Rule struct, causing
RuleList and RuleListFiltered to always return Type as 0 regardless
of the actual FIB rule action type (e.g. RTN_UNICAST, RTN_BLACKHOLE).

Add Type field to Rule struct, populate it from msg.Type during
deserialization, support setting it during rule creation, and add
RT_FILTER_TYPE filtering support.

Fixes #1055

Author: chent1996

rule.go

@@ -13,6 +13,7 @@ type Rule struct {
 	Mark              int
 	Mask              int
 	Tos               uint
+	Type              int
 	TunID             uint
 	Goto              int
 	Src               *net.IPNet

rule_linux.go

@@ -59,6 +59,9 @@ func ruleHandle(rule *Rule, req *nl.NetlinkRequest) error {
 	if rule.Tos != 0 {
 		msg.Tos = uint8(rule.Tos)
 	}
+	if rule.Type > 0 {
+		msg.Type = uint8(rule.Type)
+	}
 
 	var dstFamily uint8
 	var rtAttrs []*nl.RtAttr
@@ -225,6 +228,7 @@ func (h *Handle) RuleListFiltered(family int, filter *Rule, filterMask uint64) (
 		rule.Invert = msg.Flags&FibRuleInvert > 0
 		rule.Family = int(msg.Family)
 		rule.Tos = uint(msg.Tos)
+		rule.Type = int(msg.Type)
 
 		for j := range attrs {
 			switch attrs[j].Attr.Type {
@@ -292,6 +296,8 @@ func (h *Handle) RuleListFiltered(family int, filter *Rule, filterMask uint64) (
 				continue
 			case filterMask&RT_FILTER_TOS != 0 && rule.Tos != filter.Tos:
 				continue
+			case filterMask&RT_FILTER_TYPE != 0 && rule.Type != filter.Type:
+				continue
 			case filterMask&RT_FILTER_PRIORITY != 0 && rule.Priority != filter.Priority:
 				continue
 			case filterMask&RT_FILTER_MARK != 0 && rule.Mark != filter.Mark: