Use siphash on channel/circuit-id map too

  o Minor features (security):

    - Apply the secure SipHash-2-4 function to the hash table mapping

      circuit IDs and channels to circuits. We missed this one when we

      were converting all the other hash functions to use SipHash back

      in 0.2.5.3-alpha. Resolves ticket 11750.

static INLINE unsigned int

chan_circid_entry_hash_(chan_circid_circuit_map_t *a)

{

  return ((unsigned)a->circ_id) ^ (unsigned)(uintptr_t)(a->chan);

  struct {

    void *chan;

    circid_t circid;

  } s;

  memset(&s, 0, sizeof(s));

  s.chan = a->chan;

  s.circid = a->circ_id;

  return (unsigned) siphash24g(&s, sizeof(s));

}

/** Map from [chan,circid] to circuit. */