libceph: follow {read,write}_tier fields on osd request submission

Overwrite ceph_osd_request::r_oloc.pool with read_tier for read ops and
write_tier for write and read+write ops (aka basic tiering support).
{read,write}_tier are part of pg_pool_t since v9.  This commit bumps
our pg_pool_t decode compat version from v7 to v9, all new fields
except for {read,write}_tier are ignored.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

include/linux/ceph/osdmap.h

@@ -35,6 +35,8 @@ struct ceph_pg_pool_info {
 	u8 object_hash;
 	u32 pg_num, pgp_num;
 	int pg_num_mask, pgp_num_mask;
+	s64 read_tier;
+	s64 write_tier; /* wins for read+write ops */
 	u64 flags;
 	char *name;
 };