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.h

@@ -25,6 +25,7 @@ typedef struct VxLan VxLan;
 #include "netdev/netdev.h"
 
 #define VXLAN_VID_MAX (1u << 24) - 1
+#define VXLAN_FLOW_LABEL_MAX_MASK 0xFFFFFU
 
 struct VxLan {
         NetDev meta;
@@ -40,6 +41,7 @@ struct VxLan {
         unsigned tos;
         unsigned ttl;
         unsigned max_fdb;
+        unsigned flow_label;
 
         uint16_t dest_port;
 
@@ -94,3 +96,14 @@ int config_parse_destination_port(const char *unit,
                                   const char *rvalue,
                                   void *data,
                                   void *userdata);
+
+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);