networkd: add support for vxlan Remote and Local.

networkd: add support for vxlan Remote and Local.

This patch add supports to configure IFLA_VXLAN_LOCAL
and IFLA_VXLAN_GROUP.

The "Group" is renamed to "Remote" which is a multicast address.`

```
Description=vxlan-test
Name=vxlan1
Kind=vxlan

[VXLAN]
Id=33
Local=2001:db8:2f4:4bff:fa71:1a56
Remote=FF02:0:0:0:0:0:1:9
```

output
```
ip -d link show vxlan1
16: vxlan1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1430 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether fe:b4:97:03:f8:e5 brd ff:ff:ff:ff:ff:ff promiscuity 0
    vxlan id 33 group ff02::1:9 local 2001:db8:02f4:4bff:fa71:1a56 dev enp0s3 srcport 0 0 dstport 8472 ageing 300 noudpcsum noudp6zerocsumtx noudp6zerocsumrx addrgenmode none numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535

```