- 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]