Unfortunately I do not have any experience with IP tunneling.
But, it seems that prior you add IP tunnel, you should initialize the IP over IP tunnel device.
I would like to recommend edit rtcsinit.c file and add there:
#if RTCSCFG_ENABLE_IPIP
RTCSPROT_IPIP,
#endif
and define RTCSCFG_ENABLE_IPIP in your user_config.h file
#define RTCSCFG_ENABLE_IPIP 1
In fact, I have no idea whether this code works or not.
I am sorry.
Have a great day,
RadekS
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