Fix a bug with sdcc and icmpv6 handler

When passing function pointer without '&' code generated jumps to an invalid address when handler function is called dynamically.
I fond this issue on CC2530 with head revision of contiki an dcc2530dk plateform. I was first tracking stack issues, but finally i found that problem. Following the C norm, using '&' or not when assigning a function address to a pointer function should be the same , but it seems that with sdd it's not the case, and the code jumps to an invalid address.