netdev/ipv6: Move xxx_ipv6multicast from arch to common code

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>

net/netdev/netdev.h

@@ -495,6 +495,35 @@ void netdown_notifier_teardown(int key);
 void netdown_notifier_signal(FAR struct net_driver_s *dev);
 #endif
 
+/****************************************************************************
+ * Name: netdev_ipv6_addmcastmac/removemcastmac
+ *
+ * Description:
+ *   Add / Remove an MAC address corresponds to the IPv6 address to / from
+ *   the device's MAC filter table.
+ *
+ * Input Parameters:
+ *   dev  - The device driver structure to be modified
+ *   addr - The IPv6 address whose related MAC will be added or removed
+ *
+ * Returned Value:
+ *   None
+ *
+ * Assumptions:
+ *   The caller has locked the network.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NET_ICMPv6
+void netdev_ipv6_addmcastmac(FAR struct net_driver_s *dev,
+                             const net_ipv6addr_t addr);
+void netdev_ipv6_removemcastmac(FAR struct net_driver_s *dev,
+                                const net_ipv6addr_t addr);
+#else
+#  define netdev_ipv6_addmcastmac(dev,addr)
+#  define netdev_ipv6_removemcastmac(dev,addr)
+#endif
+
 #undef EXTERN
 #ifdef __cplusplus
 }