switch pflogd from using a bpf read timeout to a wait timeout.

switch pflogd from using a bpf read timeout to a wait timeout.

a bpf read timeout means every read will end after the timeout
expires. because pflogd has a half second read timeout it would sit
in a loop doing reads all the time even if there were no packets
to log.

the wait timeout means that when bpf catches a packet, it will wait
a bit for more packets to arrive before waking up the pending read.

pflogd now sits in the read syscall until packets are actually
available to log.

found by deraadt@ and ktrace
discussed with and ok sashan@