Point-to-Point interfaces regressions

[Li, Qing]

> 
> Li, Qing wrote:
> >> Me and many other people running net/mpd handling thousands of PtP
> >> interfaces sharing local addresses with each other and with some
> >> Ethernet interface. This change makes such setup inoperable, as mpd
> >> will constantly receive errors while trying to set addresses and
> >> drop connections.
> >
> >   I can revert to the old behavior. I asked for feedback and
received
> >   none at the time ...
> 
> I would like to see it working, but working correctly. If it is not
> possible to implement it correctly - then reverted, or at least
> disabled
> by default.
> 

  Asking for compatibility is reasonable but the existing packet 
  leaking behavior is incorrect.  

  After reviewing the previous thread on this topic back in July,
  I see that Henri Hennebert requested this feature for IPv6.

  I intend to introduce a sysctl variable to control whether loopback
  route should be installed for the local end point. By default
  the old behavior maintained.

  -- Qing