Bump __FreeBSD_version to 800043, because of the bpf(4) change.

Bump __FreeBSD_version to 800043, because of the bpf(4) change.

bpf(4) now uses cdevpriv to distinguish multiple file descriptors, where
it used to be implemented using device cloning. Ports like libpcap
properly detect the change in their configure scripts, but it doesn't
hurt to increase __FreeBSD_version.

While there, change the bpf(4) manual page to refer to /dev/bpf instead
of /dev/bpfN.

Requested by:	mlaier