This never triggerred, since send_ihu is never called with no interface.

The source table is now sorted, just like the route table.  Source insertion
is still linear, and source expiry quadratic, but this hopefully doesn't
matter much.

This appears to get rid with ENOBUFS on recvmsg.  Kill me if I know why.

Two main modifications:
  - source-specific routes are putted in front of the RIB,
  - route_stream now allows traversing all routes, all installed routes,
    or source-specific installed routes.

WLAN-SI are running into the limit.  Cool.

- We keep the "export-table" option for compatibility reasons.

- It overrides the selection of source-specific tables.  Not sure if it
  is the right thing to do.

Thanks to Jernej Kos <jernej@kos.mx> for its review.

The previous patch to only write sysctls when needed failed to restore
values that was 0 before being set by babeld. This fixes that.
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

This adds a configuration flag to skip kernel (sysctl) setup on daemon
startup. This can be useful if running in, e.g., a container environment
where setting sysctls are not allowed.
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

This reworks the sysctl handling to only write a sysctl if it is not
already the desired value. In addition, the Linux sysctl knobs are now
stored in a lookup table which is looped through, to avoid code
duplication in the setup routine.
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>