net/ndproxy: Add os-ndproxy plugin

[Monviech]

Fixes: https://github.com/opnsense/plugins/issues/3609 Fixes: https://github.com/opnsense/core/issues/7079 Requires: https://github.com/opnsense/ports/tree/master/net/ndproxy Requires: https://github.com/opnsense/core/commit/8d0ab40c56f51bb9dbbb91f2dcf73e3d6476f619

Tested with: https://pkg.opnsense.org/FreeBSD:14:amd64/snapshots/latest/All/ndproxy-3.2_1.pkg

root@opn02:~ # kldstat | grep ndproxy
34    1 0xffffffff830e8000     42fc ndproxy.ko
root@opn02:~ # sysctl -a | grep -i ndproxy
net.inet6.ndproxycount: 0
net.inet6.ndproxyconf_uplink_ipv6_addresses: fe80::;fe80::1
net.inet6.ndproxyconf_exception_ipv6_addresses: fe80::2;fe80::3
net.inet6.ndproxyconf_downlink_mac_address: 80:80:80:80:80:80
net.inet6.ndproxyconf_uplink_interface: igc0

The module provides no logs, and no statistics (that are worth the effort to display). The way it is right now, its feature complete.