ppp0: missing ipackets

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I ran into a case where ppp0's if_ipackets and if_ibytes figures (as
reported by netstat -I) were far lower than they ought to be based on
other measurements I had available.

On investigation, this proved to occur only in kernels with GATEWAY
turned on.  I believe it is probably due to

#ifdef GATEWAY
        if (ipflow_fastforward(m))
                return;
#endif

in ppp_inproc; ifp->if_ipackets and ifp->if_ibytes are updated only
later in that function.

I have verified the above by experiment only on 4.0.1, but the code is
so similar in 1.4T and 5.2, the other versions I run, that I feel
reasonably sure they have the same issue.  (Setting up a test PPP setup
under either of them would be somewhat inconvenient at present.)  I'm
mentioning it here primarily in case someone wants to check whether
-current has the same bug, secondarily so as to get this into the
archives in case someone else trips over this.

For the moment I'm just turning off GATEWAY in the kernel config.
Someday I may look for a better (FWVO "better") approach, but that is
for the future.

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