Add a log message to capture empty queue in l2c_enqueue_peer_data()

Add a log message in l2c_enqueue_peer_data() to help capture
an empty queue p_ccb->xmit_hold_q that is triggering an assert.

Also:
 * Fix a memory leak inside l2cu_initialize_fixed_ccb()
   p_ccb queues have been allocated again even though
   they have been allocated previously within l2cu_allocate_ccb()
 * Fix a typo in a comment: clodes -> closed
 * Removed repeated function declarations in file l2c_int.h

Bug: 27821847
Change-Id: I2df2843710310acf5a46c6fa5b302cf7390bc1b4