- add param.h for NetBSD [rt18228]
- use correct sysctl strings on NetBSD [rt18230]
- use net.inet.ip.portrange.hiport/hilast instead of
first/last on FreeBSD [rt18234]
- define sysctl strings for DragonFly [rt18235]
- use sysctl() on OpenBSD because it doesn't support
sysctlbyname() [rt18231]