4171 clean up spa_feature_*() interfaces
4172 implement extensible_dataset feature for use by other zpool features
Reviewed by: Max Grossman <max.grossman@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

*** 176,185 ****
--- 176,186 ----
          uint8_t dn_datablkshift;        /* zero if blksz not power of 2! */
          uint8_t dn_moved;               /* Has this dnode been moved? */
          uint16_t dn_datablkszsec;       /* in 512b sectors */
          uint32_t dn_datablksz;          /* in bytes */
          uint64_t dn_maxblkid;
+         uint8_t dn_next_type[TXG_SIZE];
          uint8_t dn_next_nblkptr[TXG_SIZE];
          uint8_t dn_next_nlevels[TXG_SIZE];
          uint8_t dn_next_indblkshift[TXG_SIZE];
          uint8_t dn_next_bonustype[TXG_SIZE];
          uint8_t dn_rm_spillblk[TXG_SIZE];       /* for removing spill blk */