aiccu: Fix typo

The option 'tunnel_id' from aiccu is called 'tunnelid' in the UCI config file. The content of $tunnelid should be checked and written to the $CFGFILE instead of the undeclared $tunnel_id.

This change was tested locally with OpenWrt Barrier Breaker 14.07-rc1.

Signed-off-by: Thomas Bahn <thomas@thomas-bahn.net>