bhyve: Add partial support for multiple config node values

[markj]

Summary

To support the slirp networking backend, it's useful to be able to
specify multiple host forwarding rules in the form
hostfwd=<rule1>,hostfwd=<rule2>,...

However, the config parser doesn't handle this possibility. Extend the
config interface to support it by adding set_config_value_node_dupok()
and a callback interface to iterate over duplicate values.

This review is just for discussion of the approach. For the slirp
backend I have another solution which simply involves using a different
delimiter: hostfwd=<rule1>;<rule2>;...

[corvink]

usr.sbin/bhyve/config.c

409–413

[jhb]

FWIW, I really would like to replace the nvlist with a tree of std::map<>. This would require converting bhyve to be a C++ binary, but only config.c would need to be a C++ file for now I think. With a suitable typedef to represent a node in place of nvlist_t I think you could hide most of that under the hood.

usr.sbin/bhyve/config.h

111

Maybe "add_config_value_node"?