picoapp icmp6 ping failed

[JsHuang]

I run the ping example using picoapp6.elf, but no matter what ipv6 address provided, the ping always failed with error 1.
Details are as below:

sudo ./build/test/picoapp6.elf --tap tap1,fe80::5cdd:5eff:fead:a691,ffff:ffff:ffff:ffff::0 --app ping,fe80::5cdd:5eff:fead:a691
My macaddr base is: ac 2c
My macaddr is: 00 00 ac 2c 0b 00
Protocol ethernet registered (layer: 2).
Protocol 6lowpan registered (layer: 2).
Protocol 6lowpan_ll registered (layer: 2).
Protocol ipv4 registered (layer: 3).
Protocol ipv6 registered (layer: 3).
Protocol icmp4 registered (layer: 4).
Protocol icmp6 registered (layer: 4).
Protocol igmp registered (layer: 4).
Protocol udp registered (layer: 4).
Protocol tcp registered (layer: 4).
dup'ing tap1
dup'ing fe80::5cdd:5eff:fead:a691
dup'ing ffff:ffff:ffff:ffff::0
Device tap1 created.
Assigned ipv4 0.0.0.0 to device tap1
+++ OPTARG ping,fe80::5cdd:5eff:fead:a691
dup'ing ping
+++ NAME: ping ARGS: fe80::5cdd:5eff:fead:a691
dup'ing fe80::5cdd:5eff:fead:a691
Starting ping.
main: launching PicoTCP loop
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
Warning: I have 21 timers
 ---- Ping6 timeout!!!
PING 1 to fe80:0000:0000:0000:5cdd:5eff:fead:a691: Error 1