[Solved] 6lowpan error: received unknown nhc id which was not found

Hi, all.

I'm developing IoT sensor working under 6lowpan bluetooth network.
The sensor also use CoAP protocol to communicate OpenWrt/LEDE router.

You could refer the following link to know my work.

Anyway, my sensor works well with 15.05-chaos calmer.
But it doesn't work with 17.04-LEDE.
(I've tested Raspberry Pi 2 and other routers with all LEDE-17.xx firmwares but failed)

I found a suspicious message in system and kernel log.
"bluetooth hci0 bt0: received unknown nhc id which was not found."

The error log comes from /linux/net/6lowpan/nhc.c.

Anyone know about this issue and any solution or even any clue ?

I found a solution.

package/kernel/linux/modules/other.mk file should be modified to load CoAP nhc module.

There is just "CONFIG_6LOWPAN_NHC=n" config to prevent build error.
If you change it to y, you meet build error.

I hope someone to make code fix and contribute it to openwrt git.
I have no skill to fix this kind of build config.