zap_allocate_blocks
newblk = zap_allocate_blocks(zap, tbl->zt_numblks * 2);
uint64_t newblk = zap_allocate_blocks(zap, 1);
l->l_blkid = zap_allocate_blocks(zap, 1);
static uint64_t zap_allocate_blocks(zap_t *zap, int nblocks);