net: ipv6_mld: Silently drop MLDv1 queries

Zephyr does not support MLDv1 (which has a shorter header than MLDv2),
and this resulted in log errors being printed on header access if MLDv1
queries were received. Since receiving such packet is not really an
error, just drop it silently.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>