lwip ipv6能接收组播包，不能ping通

[src_mac:44 a8 42 3a c7 72 ][dst_mac:33 33 00 01 00 02 ]
ethernet_input: dest:33:33:00:01:00:02, src:44:a8:42:3a:c7:72, type:86dd
33 33 00 01 00 02 44 a8   42 3a c7 72 86 dd 60 00   
00 00 00 67 11 01 fe 80   00 00 00 00 00 00 ac 84   
63 af cc c9 93 48 ff 02   00 00 00 00 00 00 00 00   
00 00 00 01 00 02 02 22   02 23 00 67 e0 9e 01 08   
a7 e0 00 08 00 02 02 bc   00 01 00 0e 00 01 00 01   
1d a8 f6 41 44 a8 42 3a   c7 72 00 03 00 0c 0e 44   
a8 42 00 00 00 00 00 00   00 00 00 27 00 11 00 0f   
44 45 4c 4c 44 45 4c 2d   4c 39 31 31 39 41 31 00   
10 00 0e 00 00 01 37 00   08 4d 53 46 54 20 35 2e   
30 00 06 00 08 00 18 00   17 00 11 00 27 5e 8e 82   
22