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
```
gperf-3.1 generates lookup functions that take a size_t length
parameter instead of unsigned int. Test for this at configure time.
Fixes: https://github.com/systemd/systemd/issues/5039
Otherwise we'd fail with an assertion:
Assertion 't->family == AF_INET' failed at ../src/network/netdev/tunnel.c:244, function netdev_vti_fill_message_create(). Aborting.
When assigning addresses, we'd set the family, and later
verify that the address on the other end has the same family.
But when the address was specified as "any", we'd simply unset
the family. Instead, only unset the family if both addresses
are wiped.
Also, don't bother setting family = AF_UNSPEC, since it's the default (0).