kernel: disable multicast-to-unicast translation for ipv6 neighbor solicitation (#17625)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

Backport of r43736

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@43737 3c298f89-4303-0410-b956-a3cf2f4a3e73