internal/router: relax dnsmasq lease file parsing condition

On DD-WRT v3.0-r52189, dnsmasq version 2.89 lease format looks like:

1685794060 <mac> <ip> <hostname> 00:00:00:00:00:04 9

It has 6 fields, while the current parser only looks for line with exact
5 fields, which is too restricted. In fact, the parser shold just skip
line with less than 4 fields, because the 4th field is the hostname,
which is the last client info that ctrld needs.

internal/router/client_info.go

@@ -105,7 +105,7 @@ func dnsmasqReadClientInfoReader(reader io.Reader) error {
 	r := routerPlatform.Load()
 	return lineread.Reader(reader, func(line []byte) error {
 		fields := bytes.Fields(line)
-		if len(fields) != 5 {
+		if len(fields) < 4 {
 			return nil
 		}
 		mac := string(fields[1])

internal/router/client_info_test.go

@@ -78,6 +78,12 @@ lease 192.168.1.2 {
 			iscDHCPReadClientInfoReader,
 			"00:00:00:00:00:02",
 		},
+		{
+			"",
+			`1685794060 00:00:00:00:00:04 192.168.0.209 cuonglm-ThinkPad-X1-Carbon-Gen-9 00:00:00:00:00:04 9`,
+			dnsmasqReadClientInfoReader,
+			"00:00:00:00:00:04",
+		},
 	}
 
 	for _, tc := range tests {