networkd: introduce vxcan netdev. (#7150)

Similar to the virtual ethernet driver veth, vxcan implements a
local CAN traffic tunnel between two virtual CAN network devices.
When creating a vxcan, two vxcan devices are created as pair
When one end receives the packet it appears on its pair and vice
versa. The vxcan can be used for cross namespace communication.

src/network/netdev/netdev.c

@@ -48,6 +48,7 @@
 #include "netdev/dummy.h"
 #include "netdev/vrf.h"
 #include "netdev/vcan.h"
+#include "netdev/vxcan.h"
 
 const NetDevVTable * const netdev_vtable[_NETDEV_KIND_MAX] = {
         [NETDEV_KIND_BRIDGE] = &bridge_vtable,
@@ -73,6 +74,7 @@ const NetDevVTable * const netdev_vtable[_NETDEV_KIND_MAX] = {
         [NETDEV_KIND_VRF] = &vrf_vtable,
         [NETDEV_KIND_VCAN] = &vcan_vtable,
         [NETDEV_KIND_GENEVE] = &geneve_vtable,
+        [NETDEV_KIND_VXCAN] = &vxcan_vtable,
 };
 
 static const char* const netdev_kind_table[_NETDEV_KIND_MAX] = {
@@ -99,6 +101,7 @@ static const char* const netdev_kind_table[_NETDEV_KIND_MAX] = {
         [NETDEV_KIND_VRF] = "vrf",
         [NETDEV_KIND_VCAN] = "vcan",
         [NETDEV_KIND_GENEVE] = "geneve",
+        [NETDEV_KIND_VXCAN] = "vxcan",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(netdev_kind, NetDevKind);