Comment the unused variable instance.
Fixed one undeclared variable. I included #include "dev/cc2420.h"//elnaz
to rpl-dag.c , however, I do not know if it is necessary or not.
We are not interested in root energy consumption. So, I deactivated the
powertracer on the root.
Minor changes
I changed the float power consumption to integer by multiplying to 8.
ETX is multiplied to 16. 
I will need to change the maximum ETX to 9 instead of 10. Unless it can
overflow the variable.
I replaced 128 with RPL_DAG_MC_ETX_DIVISOR. Because I have changed
RPL_DAG_MC_ETX_DIVISOR=16.