The `xxx_ipv6multicast` function in each driver is not adapted to
multiple IPv6 addresses yet, and they're redundant, so try to take them
into common code.
Change:
1. Add MAC `g_ipv6_ethallnodes` and `g_ipv6_ethallrouters` in
`icmpv6_devinit` and call them in `netdev_register`
2. Add multicast MAC for Neighbor Solicitation when adding any IPv6
address, and remove them when IPv6 address is removed
3. Select `NET_MCASTGROUP` when `NET_ICMPv6` because now we need
`d_addmac` when we have ICMPv6
Note:
We want modules outside net stack to call functions like
`netdev_ipv6_add` and never touch the related MAC address, so these MAC
functions are added as internal functions to `net/netdev/netdev.h`
Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>
5aeb15469a