libceph: eliminate sparse warnings

Eliminate most of the problems in the libceph code that cause sparse
to issue warnings.
    - Convert functions that are never referenced externally to have
      static scope.
    - Pass NULL rather than 0 for a pointer argument in one spot in
      ceph_monc_delete_snapid()

This partially resolves:
    http://tracker.ceph.com/issues/4184

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

net/ceph/crypto.c

@@ -423,7 +423,8 @@ int ceph_encrypt2(struct ceph_crypto_key *secret, void *dst, size_t *dst_len,
 	}
 }
 
-int ceph_key_instantiate(struct key *key, struct key_preparsed_payload *prep)
+static int ceph_key_instantiate(struct key *key,
+				struct key_preparsed_payload *prep)
 {
 	struct ceph_crypto_key *ckey;
 	size_t datalen = prep->datalen;
@@ -458,12 +459,12 @@ int ceph_key_instantiate(struct key *key, struct key_preparsed_payload *prep)
 	return ret;
 }
 
-int ceph_key_match(const struct key *key, const void *description)
+static int ceph_key_match(const struct key *key, const void *description)
 {
 	return strcmp(key->description, description) == 0;
 }
 
-void ceph_key_destroy(struct key *key) {
+static void ceph_key_destroy(struct key *key) {
 	struct ceph_crypto_key *ckey = key->payload.data;
 
 	ceph_crypto_key_destroy(ckey);

net/ceph/messenger.c

@@ -223,7 +223,7 @@ static void encode_my_addr(struct ceph_messenger *msgr)
  */
 static struct workqueue_struct *ceph_msgr_wq;
 
-void _ceph_msgr_exit(void)
+static void _ceph_msgr_exit(void)
 {
 	if (ceph_msgr_wq) {
 		destroy_workqueue(ceph_msgr_wq);

net/ceph/mon_client.c

@@ -697,7 +697,7 @@ int ceph_monc_delete_snapid(struct ceph_mon_client *monc,
 			    u32 pool, u64 snapid)
 {
 	return do_poolop(monc,  POOL_OP_CREATE_UNMANAGED_SNAP,
-				   pool, snapid, 0, 0);
+				   pool, snapid, NULL, 0);
 
 }