channel_rsa_id_group_set_badness spends a lot of time in malloc/free

in particular, a very large proportion (~25%) of allocations made seem to be "temporary", i.e. an allocation is made and then freed before any other allocations are made. possibly a portion of these are due to the second loop, but I was wondering if it is possible that the function is called with an empty list, and if that is a problem.

regardless, I have written a patch to use ht instead of only smartlists, which should very slightly increase the memory usage and moderately decrease the CPU usage in this function.