Revert "kernel: disable multicast-to-unicast translation for ipv6 neighbor solicitati...

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

This reverts commit a080e8e1943156168913d0353a2e99d1151102aa.

It did not fix the problem but just hid some symptom. The real issue was
that IGMP/MLD report suppression was not considered for the
multicast-to-unicast feature. A recent netifd which isolates IGMP/MLD
reports between STAs by utilizing AP-isolation and bridge-hairpinning
should have fixed this.

It is perfectly fine to apply multicast-to-unicast to IPv6 Neighbor
Solicitations, too (once that feature is configured correctly).

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Backport of r46720

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@47000 3c298f89-4303-0410-b956-a3cf2f4a3e73