odhcpd: Reduce error messages

odhcpd: Reduce error messages

When there's no network cable connected to LAN, then odhcpd does this:

Tue Jan 24 18:32:04 2023 daemon.err odhcpd[2017]: Failed to send to
ff02::1%lan@br-lan (Address not available)
Tue Jan 24 18:32:20 2023 daemon.err odhcpd[2017]: Failed to send to
ff02::1%lan@br-lan (Address not available)
Tue Jan 24 18:32:36 2023 daemon.err odhcpd[2017]: Failed to send to
ff02::1%lan@br-lan (Address not available)
Tue Jan 24 18:32:52 2023 daemon.err odhcpd[2017]: Failed to send to
ff02::1%lan@br-lan (Address not available)

Accurate, but not very interesting. I think this would be better served
as debug.

Signed-off-by: Peter Naulls <peter@chocky.org>