Fix issue #33: pimd does not work in background under FreeBSD

skif-kiev commented on 14 Apr:
> Being started without --debug and --foreground options pimd cant
> determine bootstrap router so doesn't send RP advertises. The reason
> is that we call `pid = getpid()` in routesock.c and use that value
> later to determine the valid message from routing socket.
>
> But between those operations we do `fork()` in main.c to daemonize
> pimd, so it gets new process ID that is different from pid. After that
> `rtm.rtm_pid != pid` becomes always true and `k_req_incoming()` always
> returns FALSE.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>