In sppp(4), allow additional 'wildcard' addresses for the destination.

In sppp(4), allow additional 'wildcard' addresses for the destination.
Any address within the range 0.0.0.1 - 0.0.0.255 can now be used.
This allows for multiple pppoe(4) interfaces with dynamic addresses within
the same routing table. Which used to work before OpenBSD 5.8, but since 5.8
only one interface in a routing table can use destination address 0.0.0.1.

Problem first reported by Steve (fiverings04 at australian yahoo) on misc@.
I ran into it on an EdgeRouter lite which is supposed to serve two ADSL lines.
ok sthen@ mpi@
man page help from jmc@ for an earlier variant of this change