There is a new kernel option PPP_FILTER to enable bpf based filtering.
This was enabled by default in the previous version of pppd. If you
are using the "active-filter" and "pass-filter" options in your ppp
options file, you need this. I've made this a separate option, because
Paul Mackerras removed it from the ppp distribution (but I think he
will put it back).

Please report problems to me.