[kfreebsd] Remove some leftovers.
[kfreebsd] Fix parsing of the mirage.maxmem kenv(1) variable.
[kfreebsd] Remove a leftover function from `OS.Netif`.
[kfreebsd] Fix random number generation.
[kfreebsd] Be more careful with finalizing custom blocks left on the heap.
[kfreebsd] Enable multiple instances (and netgraph(3)) to co-exist on the same host.