Add multiple unicast destinations to vxlan

[ben_desync.com]

Summary

Extend the current support for VXLAN over unicast to allow for multiple remote hosts.

This enables VXLAN with more than two participants without requiring multicast.

Test Plan

ifconfig vxlan0 vxlanremote 10.0.0.2
ifconfig vxlan0 vxlanremote 10.0.0.3
ifconfig -v vxlan0
ifconfig vxlan0 -vxlanremote 10.0.0.3

[bryanv]

sys/net/if_vxlan.c

940

You can remove this check because it will be automatically handled below

949

Generally, the FreeBSD style is to omit returns statements like this.

[ben_desync.com]

Updated to address feedback
Thanks!