networkd: vxlan support setting IPv6 flow labe

This work adds support for setting the IPv6 flow label for vxlan.

vxlan.netdev

NetDev]
Description=vxlan-test
Name=vxlan1
Kind=vxlan

[VXLAN]
Id=33
Local=2405:204:920b:29ac:7e7a:91ff:fe6d:ffe2
Remote=FF02:0:0:0:0:0:1:9
FlowLabel=104
ip -d link show vxlan1

8: vxlan1: <BROADCAST,MULTICAST> mtu 1430 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether be:83:aa:db:6b:cb brd ff:ff:ff:ff:ff:ff promiscuity 0
    vxlan id 33 group ff02::1:9 local 2405:204:920b:29ac:7e7a:91ff:fe6d:ffe2 dev enp0s25 srcport 0 0 dstport 8472 flowlabel 0x68 ageing 300 noudpcsum noudp6zerocsumtx noudp6zerocsumrx addrgenmode eui64 numtxqueues 1 numrxqueues 1

src/network/netdev/vxlan.c

@@ -157,6 +157,10 @@ static int netdev_vxlan_fill_message_create(NetDev *netdev, Link *link, sd_netli
                         return log_netdev_error_errno(netdev, r, "Could not append IFLA_VXLAN_PORT_RANGE attribute: %m");
         }
 
+        r = sd_netlink_message_append_u32(m, IFLA_VXLAN_LABEL, htobe32(v->flow_label));
+        if (r < 0)
+                return log_netdev_error_errno(netdev, r, "Could not append IFLA_VXLAN_LABEL attribute: %m");
+
         if (v->group_policy) {
                 r = sd_netlink_message_append_flag(m, IFLA_VXLAN_GBP);
                 if (r < 0)
@@ -297,6 +301,42 @@ int config_parse_destination_port(const char *unit,
         return 0;
 }
 
+int config_parse_flow_label(const char *unit,
+                            const char *filename,
+                            unsigned line,
+                            const char *section,
+                            unsigned section_line,
+                            const char *lvalue,
+                            int ltype,
+                            const char *rvalue,
+                            void *data,
+                            void *userdata) {
+        VxLan *v = userdata;
+        unsigned f;
+        int r;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(data);
+
+        r = safe_atou(rvalue, &f);
+        if (r < 0) {
+                log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse VXLAN flow label '%s'.", rvalue);
+                return 0;
+        }
+
+        if (f & ~VXLAN_FLOW_LABEL_MAX_MASK) {
+                log_syntax(unit, LOG_ERR, filename, line, r,
+                           "VXLAN flow label '%s' not valid. Flow label range should be [0-1048575].", rvalue);
+                return 0;
+        }
+
+        v->flow_label = f;
+
+        return 0;
+}
+
 static int netdev_vxlan_verify(NetDev *netdev, const char *filename) {
         VxLan *v = VXLAN(netdev);