This avoids a network meltdown in extreme cases.
Thanks to Teco Boot.

When adding a network interface that is already known to babeld, an
error message is displayed and the new configuration is ignored. This
message is adjusted to include the name of the interface being added so
it is visible from the logs without context

This removes a duplicate call to local_notify_interface(ifp, LOCAL_FLUSH)
which lead to duplicate output on the monitoring socket.

It was essentially a no-op with an inverted test.

This reverts commit 005f1197.

Thanks to Dave Taht for the report.

Now that we can carry more routes, try to carry them.

A late hello is an early warning sign of a cpu overload or
overbuffering.

Only set rp_filter to 0 if it contains a different value when
initializing new interfaces. This is helpful to run babeld inside docker
without --privileged

Thanks to Dave Taht.

This allows walking the two lists in parallel.

Use binary search to locate an xroute.

Reported by cppcheck.

(portability) '(void*)((char*)current_attribute)' is of type
'void *'. When using void pointers in calculations, the behaviour is
undefined.

We can no longer call send_multihop_request with a NULL argument.

This removes duplication between unicast and multicast variants of message
formatting.