Always send hood to Monitoring

Since the MacNocker was introduced, the hood information in
UCI is DELETED if the hood is lost.

If the router still successfully sends alfred data in this state,
the Monitoring will treat it as a V1 device. This is annoying,
especially since it looks like a loop.

An easy solution is to send an empty <hood> field in those cases,
as V2 routers are detected by them knowing their hood.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Tim Niemeyer <tim@tn-x.org>