RIP v1 handling

[Krzysztof Strasburger]

Dear maintainers of zebra!
This is not a real bug report, but...
I'm using zebra version 0.93a. It works well, but it receives a lot of
RIP v1 packets from two old Netware 3.11 routers and guesses incorrectly
the netmask. For RIP v1 it gives always an netmask appropriate for some
class of networks and does not try to guess the real subnet mask. I did
a quick hack - the function if_valid neighbor returns the length of mask
of the segment the packet came from, and the further code assumes that
this netmask is the same as for the segments behind the router (which is
true in my case). This approach works well for me, but i'm aware of the
fact that there is no universal method of guessing the real netmask for
RIP v1. I would consider choosing the method via a configuration option.
Thank you for zebra
Krzysztof Strasburger