(while Social Security benefits constitute "gross income" for purposes of Chapter 12 only to the extent provided in the tax code, and "qualified military benefits" are excluded from gross income, debtor did not establish that any of his military benefits were "qualified military benefits as defined in the tax code, and that even with excluding debtor's average monthly Social Security income, debtor still did not have more than one-half of his income from farming in each of the second and third years preceding petition date or in the year preceding filing Chapter 12; debtor ineligible for Chapter 12 relief).