wallet2: fix sweep_unmixable assuming wrong minimum mixin at v5

The bump to minimum mixin 4 was moved from v5 to v6

src/wallet/wallet2.cpp

@@ -4889,14 +4889,14 @@ const wallet2::transfer_details &wallet2::get_transfer_details(size_t idx) const
 std::vector<size_t> wallet2::select_available_unmixable_outputs(bool trusted_daemon)
 {
   // request all outputs with less than 3 instances
-  const size_t min_mixin = use_fork_rules(5, 10) ? 4 : 2; // v5 increases min mixin from 2 to 4
+  const size_t min_mixin = use_fork_rules(6, 10) ? 4 : 2; // v6 increases min mixin from 2 to 4
   return select_available_outputs_from_histogram(min_mixin + 1, false, true, false, trusted_daemon);
 }
 //----------------------------------------------------------------------------------------------------
 std::vector<size_t> wallet2::select_available_mixable_outputs(bool trusted_daemon)
 {
   // request all outputs with at least 3 instances, so we can use mixin 2 with
-  const size_t min_mixin = use_fork_rules(5, 10) ? 4 : 2; // v5 increases min mixin from 2 to 4
+  const size_t min_mixin = use_fork_rules(6, 10) ? 4 : 2; // v6 increases min mixin from 2 to 4
   return select_available_outputs_from_histogram(min_mixin + 1, true, true, true, trusted_daemon);
 }
 //----------------------------------------------------------------------------------------------------