Bug #642: Use fine grain locking in smp mode in net layer
Changed CmiCommlock to finer grain locks; send_queue_lock,
Cmi_freelist_mutex and Cmi_comm_var_mutex.
send_queue_lock is for each of the outgoing msg queues where worker threads
drops the messages and comm thread consumes.
Cmi_freelist_mutex is for the shared free list where the used datagrams are stored and reused.
Cmi_comm_var_mutex is for protecting other variables that worker and comm
thread share such as writeableDgrams.
Change-Id: I08f8cf71846d91dd48afd28bd0ad83447f5ba0d4